# Gladius
**Parse, don't validate.** `conform/2` returns a *shaped* value on success — coercions applied, transforms run, data restructured — not just `true`. Specs are composable structs, not modules. Write a spec once; use it to validate, generate test data, check function signatures, and produce typespecs.
[](https://hex.pm/packages/gladius)
[](https://hexdocs.pm/gladius)
---
## Contents
- [Installation](#installation)
- [Quick Start](#quick-start)
- [Primitives](#primitives)
- [Named Constraints](#named-constraints)
- [Combinators](#combinators)
- [Schemas](#schemas)
- [Default Values](#default-values)
- [Post-Validation Transforms](#post-validation-transforms)
- [Struct Validation](#struct-validation)
- [Registry](#registry)
- [Coercion](#coercion)
- [Generators](#generators)
- [Function Signatures](#function-signatures)
- [Typespec Bridge](#typespec-bridge)
- [Testing](#testing)
- [Compared to Alternatives](#compared-to-alternatives)
- [AI Agent Reference](#ai-agent-reference)
---
## Installation
```elixir
# mix.exs
def deps do
[
{:gladius, "~> 0.2"}
]
end
```
Gladius runs a registry under its own supervision tree — no configuration needed; it starts automatically with your application.
---
## Quick Start
```elixir
import Gladius
user = schema(%{
required(:name) => string(:filled?),
required(:email) => string(:filled?, format: ~r/@/),
required(:age) => integer(gte?: 18),
optional(:role) => atom(in?: [:admin, :user, :guest])
})
Gladius.conform(user, %{name: "Mark", email: "mark@x.com", age: 33})
#=> {:ok, %{name: "Mark", email: "mark@x.com", age: 33}}
Gladius.conform(user, %{name: "", age: 15})
#=> {:error, [
#=> %Gladius.Error{path: [:name], message: "must be filled"},
#=> %Gladius.Error{path: [:email], message: "key :email must be present"},
#=> %Gladius.Error{path: [:age], message: "must be >= 18"}
#=> ]}
```
**Three entry points:**
| Function | Returns |
|----------|---------|
| `Gladius.conform(spec, value)` | `{:ok, shaped_value}` or `{:error, [Error.t()]}` |
| `Gladius.valid?(spec, value)` | `boolean()` |
| `Gladius.explain(spec, value)` | `ExplainResult.t()` with a formatted string |
```elixir
result = Gladius.explain(user, %{name: "", age: 15})
result.valid? #=> false
IO.puts result.formatted
# :name: must be filled
# :email: key :email must be present
# :age: must be >= 18
```
---
## Primitives
```elixir
import Gladius
string() # any binary
integer() # any integer
float() # any float
number() # integer or float
boolean() # true or false
atom() # any atom
map() # any map
list() # any list
any() # any value — always conforms
nil_spec() # nil only
```
---
## Named Constraints
Named constraints are introspectable (the generator can read them) and composable.
```elixir
# String constraints
string(:filled?) # non-empty
string(min_length: 3) # byte length >= 3
string(max_length: 50) # byte length <= 50
string(size?: 5) # byte length == 5
string(format: ~r/^\d{4}$/) # regex match
string(:filled?, format: ~r/@/) # shorthand atom + keyword list
# Integer constraints
integer(gt?: 0) # > 0
integer(gte?: 0) # >= 0 (→ non_neg_integer() in typespec)
integer(gt?: 0, lte?: 100) # 1 to 100
integer(gte?: 1, lte?: 100) # → 1..100 in typespec
integer(in?: [1, 2, 3]) # membership
# Float constraints
float(gt?: 0.0)
float(gte?: 0.0, lte?: 1.0)
# Atom constraints
atom(in?: [:admin, :user, :guest]) # → :admin | :user | :guest in typespec
```
---
## Combinators
### `all_of/1` — intersection
All specs must conform. The **output** of each is the **input** to the next — enabling lightweight transformation pipelines.
```elixir
all_of([integer(), spec(&(&1 > 0))]) # positive integer
all_of([string(), string(:filled?)]) # non-empty string
all_of([
coerce(integer(), from: :string), # coerce string → integer
spec(&(rem(&1, 2) == 0)) # then check even
])
```
### `any_of/1` — union
Tries specs in order, returns the first success.
```elixir
any_of([integer(), string()]) # accepts integer or string
any_of([nil_spec(), integer()]) # nullable integer (prefer maybe/1)
```
### `not_spec/1` — complement
```elixir
all_of([string(), not_spec(string(:filled?))]) # empty string only
```
### `maybe/1` — nullable
`nil` passes unconditionally. Non-nil values are validated against the inner spec.
```elixir
maybe(string(:filled?)) # nil or non-empty string
maybe(integer(gte?: 0)) # nil or non-negative integer
maybe(ref(:address)) # nil or a valid address schema
```
### `list_of/1` — typed list
Validates every element. Errors **accumulate across all elements** — no short-circuiting.
```elixir
list_of(integer(gte?: 0))
# [1, 2, 3] → {:ok, [1, 2, 3]}
# [1, -1, 3] → {:error, [%Error{path: [1], message: "must be >= 0"}]}
# [1, -1, -2] → {:error, [errors at index 1 and index 2]}
```
### `cond_spec/2-3` — conditional branching
Applies one branch based on a predicate.
```elixir
cond_spec(
fn order -> order.type == :physical end,
ref(:address_schema),
nil_spec()
)
# else_spec defaults to any() if omitted
cond_spec(&is_binary/1, string(:filled?))
```
### `spec/1` — arbitrary predicate
```elixir
spec(&is_integer/1)
spec(&(&1 > 0))
spec(fn n -> rem(n, 2) == 0 end)
spec(is_integer() and &(&1 > 0))
spec(&is_integer/1, gen: StreamData.integer(1..1000))
```
### `coerce/2` — coercion wrapper
See [Coercion](#coercion) for the full reference.
```elixir
coerce(integer(gte?: 0), from: :string) # parse then validate
maybe(coerce(integer(), from: :string)) # nil passes; string coerces
list_of(coerce(integer(), from: :string)) # coerce every element
```
---
## Schemas
### `schema/1` — closed map
Extra keys not declared in the schema are rejected. Errors **accumulate across all keys** in one pass.
```elixir
user_schema = schema(%{
required(:name) => string(:filled?),
required(:email) => string(:filled?, format: ~r/@/),
required(:age) => integer(gte?: 0),
optional(:role) => atom(in?: [:admin, :user]),
optional(:address) => schema(%{
required(:street) => string(:filled?),
required(:zip) => string(size?: 5)
})
})
```
### `open_schema/1` — extra keys pass through
```elixir
base = open_schema(%{required(:id) => integer(gt?: 0)})
Gladius.conform(base, %{id: 1, extra: "anything"})
#=> {:ok, %{id: 1, extra: "anything"}}
```
### `ref/1` — lazy registry reference
Resolved at conform-time. Enables circular schemas.
```elixir
defspec :tree_node, schema(%{
required(:value) => integer(),
optional(:children) => list_of(ref(:tree_node))
})
```
---
## Default Values
`default/2` injects a fallback value when an optional key is absent. The fallback is injected as-is — the inner spec only runs when the key is **present**.
```elixir
schema(%{
required(:name) => string(:filled?),
optional(:role) => default(atom(in?: [:admin, :user, :guest]), :user),
optional(:retries) => default(integer(gte?: 0), 3),
optional(:tags) => default(list_of(string(:filled?)), [])
})
Gladius.conform(schema, %{name: "Mark"})
#=> {:ok, %{name: "Mark", role: :user, retries: 3, tags: []}}
```
**Semantics:**
- Key absent → fallback injected directly; inner spec not run
- Key present → inner spec validates the provided value normally
- Invalid provided value → error returned; default does not rescue it
- Required key → `default/2` has no effect on absence; missing required keys always error
`default/2` accepts any conformable as its inner spec:
```elixir
optional(:coords) => default(schema(%{required(:x) => integer()}), %{x: 0})
optional(:ref) => default(maybe(string(:filled?)), nil)
optional(:wrapped) => default(ref(:address), %{street: "unknown", zip: "00000"})
```
---
## Post-Validation Transforms
`transform/2` applies a function to the shaped value **after** validation succeeds. It never runs on invalid data.
**Pipeline:** `raw → coerce → validate → transform → {:ok, result}`
```elixir
# Normalize strings at the boundary
email_spec = transform(string(:filled?, format: ~r/@/), &String.downcase/1)
name_spec = transform(string(:filled?), &String.trim/1)
schema(%{
required(:name) => name_spec,
required(:email) => email_spec
})
Gladius.conform(schema, %{name: " Mark ", email: "MARK@X.COM"})
#=> {:ok, %{name: "Mark", email: "mark@x.com"}}
```
Chain transforms with pipe — `transform/2` is spec-first for exactly this reason:
```elixir
string(:filled?)
|> transform(&String.trim/1)
|> transform(&String.downcase/1)
```
Enrich a schema output:
```elixir
transform(
schema(%{required(:name) => string(:filled?)}),
fn m -> Map.put(m, :slug, String.downcase(m.name)) end
)
```
**Error handling:** if the transform function raises, the exception is caught and returned as `%Gladius.Error{predicate: :transform, message: "transform failed: ..."}`. The caller never crashes.
**With defaults:** when `default/2` wraps a `transform/2`, the default value bypasses the transform entirely (consistent with bypassing the inner spec):
```elixir
optional(:name) => default(transform(string(:filled?), &String.trim/1), "anon")
# key absent → "anon" injected, trim never runs
# key present → trimmed and validated normally
```
---
## Struct Validation
### Structs as input to `conform/2`
`conform/2` accepts any Elixir struct directly — no `Map.from_struct/1` needed. The output is a plain map.
```elixir
defmodule User do
defstruct [:name, :email, :age]
end
s = schema(%{
required(:name) => transform(string(:filled?), &String.trim/1),
required(:email) => string(:filled?, format: ~r/@/)
})
Gladius.conform(s, %User{name: " Mark ", email: "mark@x.com"})
#=> {:ok, %{name: "Mark", email: "mark@x.com"}}
```
`valid?/2` and `explain/2` accept structs the same way.
### `conform_struct/2` — validate and re-wrap
When you need the shaped output back in the original struct type:
```elixir
Gladius.conform_struct(s, %User{name: " Mark ", email: "mark@x.com"})
#=> {:ok, %User{name: "Mark", email: "mark@x.com"}}
```
Coercions and transforms are reflected in the returned struct:
```elixir
s = schema(%{
required(:name) => transform(string(:filled?), &String.trim/1),
required(:age) => coerce(integer(), from: :string)
})
Gladius.conform_struct(s, %User{name: " Mark ", age: "33"})
#=> {:ok, %User{name: "Mark", age: 33}}
```
Errors are the same `{:error, [%Gladius.Error{}]}` format as `conform/2`. A plain map (non-struct) input returns an error immediately.
### `defschema struct: true` — schema + struct in one
Defines the validator functions **and** a matching output struct in a single declaration. The struct module is named `<CallerModule>.<PascalName>Schema`.
```elixir
defmodule MyApp.Schemas do
import Gladius
defschema :point, struct: true do
schema(%{
required(:x) => integer(),
required(:y) => integer()
})
end
defschema :person, struct: true do
schema(%{
required(:name) => transform(string(:filled?), &String.trim/1),
optional(:score) => default(integer(gte?: 0), 0)
})
end
end
MyApp.Schemas.point(%{x: 3, y: 4})
#=> {:ok, %MyApp.Schemas.PointSchema{x: 3, y: 4}}
MyApp.Schemas.person(%{name: " Mark "})
#=> {:ok, %MyApp.Schemas.PersonSchema{name: "Mark", score: 0}}
MyApp.Schemas.point!(%{x: "bad", y: 0})
#=> raises Gladius.ConformError
```
Transforms run before struct wrapping; defaults are injected before struct wrapping.
---
## Registry
### `defspec` — globally named spec
```elixir
defmodule MyApp.Specs do
import Gladius
defspec :email, string(:filled?, format: ~r/@/)
defspec :username, string(:filled?, min_length: 3, max_length: 32)
defspec :age, integer(gte?: 0, lte?: 150)
defspec :role, atom(in?: [:admin, :user, :guest])
end
```
Reference with `ref/1` from anywhere:
```elixir
schema(%{
required(:email) => ref(:email),
required(:username) => ref(:username),
required(:age) => ref(:age),
optional(:role) => ref(:role)
})
```
### `defschema` — named validator functions
Generates `name/1` → `{:ok, shaped} | {:error, errors}` and `name!/1` → shaped value or raises `ConformError`.
```elixir
defmodule MyApp.Schemas do
import Gladius
defschema :user do
schema(%{
required(:name) => string(:filled?),
required(:email) => ref(:email),
required(:age) => integer(gte?: 18),
optional(:role) => atom(in?: [:admin, :user])
})
end
defschema :create_params do
schema(%{
required(:email) => coerce(ref(:email), from: :string),
required(:age) => coerce(integer(gte?: 18), from: :string)
})
end
end
MyApp.Schemas.user(%{name: "Mark", email: "m@x.com", age: 33})
#=> {:ok, %{name: "Mark", email: "m@x.com", age: 33}}
MyApp.Schemas.user!(%{name: "", age: 15})
#=> raises Gladius.ConformError
```
---
## Coercion
`coerce/2` wraps a spec with a pre-processing step.
**Pipeline:** `raw value → coerce → type check → constraints → {:ok, coerced value}`
Coercion failure produces `%Error{predicate: :coerce}` and skips downstream checks.
### Custom function
```elixir
coerce(integer(), fn
v when is_binary(v) ->
case Integer.parse(String.trim(v)) do
{n, ""} -> {:ok, n}
_ -> {:error, "not a valid integer string: #{inspect(v)}"}
end
v when is_integer(v) -> {:ok, v}
v -> {:error, "cannot coerce #{inspect(v)} to integer"}
end)
```
### Built-in shorthand — `from: source_type`
All built-in coercions are **idempotent** — already-correct values pass through unchanged.
```elixir
coerce(integer(), from: :string) # "42" → 42
coerce(float(), from: :string) # "3.14" → 3.14
coerce(boolean(), from: :string) # "true" → true (yes/1/on also work)
coerce(atom(), from: :string) # "ok" → :ok (existing atoms only)
coerce(float(), from: :integer) # 42 → 42.0
coerce(string(), from: :integer) # 42 → "42"
coerce(boolean(), from: :integer) # 0 → false, 1 → true
coerce(string(), from: :atom) # :ok → "ok"
coerce(integer(), from: :float) # 3.7 → 3
coerce(string(), from: :float) # 3.14 → "3.14"
```
### User-extensible coercion registry
```elixir
Gladius.Coercions.register({:decimal, :float}, fn
%Decimal{} = d -> {:ok, Decimal.to_float(d)}
v when is_float(v) -> {:ok, v}
v -> {:error, "cannot coerce #{inspect(v)} to float"}
end)
coerce(float(gt?: 0.0), from: :decimal)
```
### Composition patterns
```elixir
# HTTP params / form data
http_params = schema(%{
required(:age) => coerce(integer(gte?: 18), from: :string),
required(:active) => coerce(boolean(), from: :string),
required(:score) => coerce(float(gt?: 0.0), from: :string),
optional(:role) => coerce(atom(in?: [:admin, :user]), from: :string)
})
Gladius.conform(http_params, %{age: "25", active: "true", score: "9.5", role: "admin"})
#=> {:ok, %{age: 25, active: true, score: 9.5, role: :admin}}
# Coerce every list element
list_of(coerce(integer(), from: :string))
# ["1", "2", "3"] → {:ok, [1, 2, 3]}
```
---
## Generators
`gen/1` infers a `StreamData` generator from any spec. Available in `:dev` and `:test` — zero overhead in `:prod`.
```elixir
gen(string(:filled?))
gen(integer(gte?: 0, lte?: 100))
gen(atom(in?: [:admin, :user]))
gen(maybe(integer()))
gen(list_of(string(:filled?)))
gen(any_of([integer(), string()]))
gen(schema(%{required(:name) => string(:filled?), required(:age) => integer(gte?: 0)}))
gen(default(integer(gte?: 0), 0)) # delegates to inner spec
gen(transform(integer(), &(&1 * 2))) # delegates to inner spec
```
Use with `ExUnitProperties`:
```elixir
defmodule MyApp.PropertyTest do
use ExUnitProperties
import Gladius
property "conform is idempotent for valid values" do
spec = schema(%{
required(:email) => string(:filled?, format: ~r/@/),
required(:age) => integer(gte?: 0, lte?: 150)
})
check all value <- gen(spec) do
{:ok, shaped} = Gladius.conform(spec, value)
assert Gladius.conform(spec, shaped) == {:ok, shaped}
end
end
end
```
---
## Function Signatures
`use Gladius.Signature` enables runtime validation in `:dev` and `:test`. **Zero overhead in `:prod`.**
```elixir
defmodule MyApp.Users do
use Gladius.Signature
signature args: [string(:filled?), integer(gte?: 18)],
ret: boolean()
def register(email, age) do
true
end
end
MyApp.Users.register("mark@x.com", 33) #=> true
MyApp.Users.register("", 33) #=> raises SignatureError
```
### Options
| Key | Validates |
|-----|-----------|
| `:args` | List of specs, one per argument, positional |
| `:ret` | Return value |
| `:fn` | `{coerced_args_list, return_value}` — input/output relationships |
### Coercion threading
When `:args` specs include coercions, **coerced values are forwarded to the impl**.
```elixir
signature args: [coerce(integer(gte?: 0), from: :string)],
ret: string()
def double(n), do: Integer.to_string(n * 2)
MyApp.double("5") #=> "10"
```
### Path errors
All failing arguments are collected in one raise, with full nested paths:
```elixir
signature args: [schema(%{
required(:email) => string(:filled?, format: ~r/@/),
required(:name) => string(:filled?)
})],
ret: boolean()
def create(params), do: true
MyApp.create(%{email: "bad", name: ""})
# raises Gladius.SignatureError:
# argument[0][:email]: format must match ~r/@/
# argument[0][:name]: must be filled
```
---
## Typespec Bridge
```elixir
Macro.to_string(Gladius.to_typespec(integer(gte?: 0))) #=> "non_neg_integer()"
Macro.to_string(Gladius.to_typespec(integer(gt?: 0))) #=> "pos_integer()"
Macro.to_string(Gladius.to_typespec(integer(gte?: 1, lte?: 100))) #=> "1..100"
Macro.to_string(Gladius.to_typespec(atom(in?: [:a, :b]))) #=> ":a | :b"
Macro.to_string(Gladius.to_typespec(maybe(string()))) #=> "String.t() | nil"
Macro.to_string(Gladius.to_typespec(default(integer(), 0))) #=> "integer()"
Macro.to_string(Gladius.to_typespec(transform(string(), &String.trim/1))) #=> "String.t()"
```
### `@type` generation
```elixir
defspec :user_id, integer(gte?: 1), type: true
# @type user_id :: pos_integer()
defschema :profile, type: true do
schema(%{
required(:name) => string(:filled?),
required(:age) => integer(gte?: 0),
optional(:role) => atom(in?: [:admin, :user])
})
end
# @type profile :: %{required(:name) => String.t(),
# required(:age) => non_neg_integer(),
# optional(:role) => :admin | :user}
```
---
## Testing
### Process-local registry for async tests
```elixir
defmodule MyApp.SpecTest do
use ExUnit.Case, async: true
import Gladius
setup do
on_exit(&Gladius.Registry.clear_local/0)
:ok
end
test "ref resolves to a locally registered spec" do
Gladius.Registry.register_local(:test_email, string(:filled?, format: ~r/@/))
spec = schema(%{required(:email) => ref(:test_email)})
assert {:ok, _} = Gladius.conform(spec, %{email: "a@b.com"})
assert {:error, _} = Gladius.conform(spec, %{email: "bad"})
end
end
```
### Property-based testing
```elixir
property "generated values always conform" do
spec = schema(%{
required(:name) => string(:filled?),
required(:age) => integer(gte?: 0, lte?: 150),
optional(:score) => float(gte?: 0.0, lte?: 1.0)
})
check all value <- gen(spec) do
assert {:ok, _} = Gladius.conform(spec, value)
end
end
```
---
## Compared to Alternatives
| | gladius | Norm | Drops | Peri |
|-|--------|------|-------|------|
| Parse, don't validate | ✓ | ✓ | ✓ | ✓ |
| Named constraints | ✓ | — | ✓ | ✓ |
| Generator inference | ✓ | — | — | — |
| Function signatures | ✓ | ✓ | — | — |
| Coercion pipeline | ✓ | — | ✓ | — |
| User coercion registry | ✓ | — | — | — |
| Default values | ✓ | — | — | ✓ |
| Post-validation transforms | ✓ | — | — | — |
| Struct validation | ✓ | — | — | — |
| Ecto integration | ✓ | — | — | ✓ |
| Typespec bridge | ✓ | — | — | — |
| `@type` generation | ✓ | — | — | — |
| Circular schemas (`ref`) | ✓ | — | — | — |
| Prod zero-overhead signatures | ✓ | — | ✓ | ✓ |
| Accumulating schema errors | ✓ | ✓ | ✓ | ✓ |
---
## AI Agent Reference
### Module map
| Module | Purpose |
|--------|---------|
| `Gladius` | Primary API — `import Gladius` |
| `Gladius.Signature` | Function signature validation — `use Gladius.Signature` |
| `Gladius.Typespec` | Spec → typespec AST conversion |
| `Gladius.Coercions` | Coercion functions + user registry |
| `Gladius.Registry` | Named spec registry (ETS + process-local) |
| `Gladius.Gen` | Generator inference (dev/test only) |
| `Gladius.Error` | Validation failure struct |
| `Gladius.SignatureError` | Raised on signature violation |
| `Gladius.ConformError` | Raised by `defschema name!/1` |
### Complete `Gladius` function signatures
```elixir
# Primitive builders (all accept keyword constraints)
string() | string(atom) | string(atom, kw) | string(kw)
integer() | integer(atom) | integer(atom, kw) | integer(kw)
float() | float(atom) | float(atom, kw) | float(kw)
number() | boolean() | map() | list() | any() | nil_spec()
atom() | atom(kw)
# Combinators
all_of([conformable()]) :: All.t()
any_of([conformable()]) :: Any.t()
not_spec(conformable()) :: Not.t()
maybe(conformable()) :: Maybe.t()
list_of(conformable()) :: ListOf.t()
cond_spec(pred_fn, if_spec) :: Cond.t()
cond_spec(pred_fn, if_spec, else_spec) :: Cond.t()
coerce(Spec.t(), (term -> {:ok, t} | {:error, s})) :: Spec.t()
coerce(Spec.t(), from: source_atom) :: Spec.t()
default(conformable(), term()) :: Default.t()
transform(conformable(), (term() -> term())) :: Transform.t()
ref(atom) :: Ref.t()
spec(pred_or_guard_expr) :: Spec.t()
spec(pred_or_guard_expr, gen: StreamData.t()) :: Spec.t()
# Schema
schema(%{schema_key => conformable()}) :: Schema.t()
open_schema(%{schema_key => conformable()}) :: Schema.t()
required(atom)
optional(atom)
# Registration (macros)
defspec name_atom, spec_expr
defspec name_atom, spec_expr, type: true
defschema name_atom do spec_expr end
defschema name_atom, type: true do spec_expr end
defschema name_atom, struct: true do spec_expr end
# Validation
Gladius.conform(conformable(), term()) :: {:ok, term()} | {:error, [Error.t()]}
Gladius.conform_struct(conformable(), struct()) :: {:ok, struct()} | {:error, [Error.t()]}
Gladius.valid?(conformable(), term()) :: boolean()
Gladius.explain(conformable(), term()) :: ExplainResult.t()
# Generator (dev/test only)
Gladius.gen(conformable()) :: StreamData.t()
# Typespec
Gladius.to_typespec(conformable()) :: Macro.t()
Gladius.typespec_lossiness(conformable()) :: [{atom(), String.t()}]
Gladius.Typespec.type_ast(atom, conformable()) :: Macro.t()
```
### All named constraints by type
```
# String
:filled? non-empty — byte_size > 0
min_length: n byte_size >= n
max_length: n byte_size <= n
size?: n byte_size == n
format: ~r/regex/ must match regex
# Integer / Float / Number
gt?: n > n
gte?: n >= n
lt?: n < n
lte?: n <= n
in?: [values] member of list (integer or atom)
# Atom
in?: [atoms] member of atom list
```
### All built-in coercion pairs
```
{:string, :integer}
{:string, :float}
{:string, :boolean} true/yes/1/on → true; false/no/0/off → false
{:string, :atom} String.to_existing_atom — safe
{:string, :number} same as {:string, :float}
{:integer, :float}
{:integer, :string}
{:integer, :boolean} 0 → false, 1 → true; others → error
{:atom, :string} nil → error (nil is an atom in Elixir)
{:float, :integer} trunc/1 — truncates toward zero
{:float, :string}
```
All coercions are idempotent.
### `default/2` semantics
```
default(spec, value)
Key absent + optional → value injected; spec not run
Key absent + required → missing-key error; default ignored
Key present → spec validates the provided value; value ignored
Invalid provided value → error returned; value does not rescue it
Ref pointing to Default → resolved at conform-time; default injection works
```
### `transform/2` semantics
```
transform(spec, fun)
Pipeline: raw → conform(spec) → fun.(shaped) → {:ok, result}
Validation fails → {:error, errors} passed through; fun never called
fun.(shaped) raises → {:error, [%Error{predicate: :transform, ...}]}
fun.(shaped) ok → {:ok, fun_return_value}
Chaining: spec |> transform(f) |> transform(g) — g receives output of f
With coerce: coerce runs before validate; transform runs after
With default: absent key bypasses both inner spec and transform
```
### `conform_struct/2` semantics
```
conform_struct(spec, struct)
Non-struct input → {:error, [%Error{message: "conform_struct/2 requires a struct..."}]}
Valid struct → {:ok, struct(original_module, shaped_map)}
Invalid struct → {:error, [%Gladius.Error{}]} — same format as conform/2
```
### `defschema struct: true` behaviour
```
defschema :point, struct: true do
schema(%{required(:x) => integer(), required(:y) => integer()})
end
Generated:
- Module <CallerModule>.PointSchema with defstruct [:x, :y]
- def point(data) :: {:ok, %PointSchema{}} | {:error, [Error.t()]}
- def point!(data) :: %PointSchema{} | raises ConformError
Struct field names derived from schema key names at compile time.
Transforms and defaults run before struct wrapping.
```
### `Gladius.Error` struct
```elixir
%Gladius.Error{
path: [atom() | non_neg_integer()],
predicate: atom() | nil,
# :filled?, :gte?, :gt?, :lte?, :lt?, :format, :in?,
# :min_length, :max_length, :size?, :coerce, :transform
value: term(),
message: String.t(),
meta: map()
}
```
### Type union — the `conformable()` type
```
conformable() =
Gladius.Spec # primitives and coerce wrappers
| Gladius.All # all_of
| Gladius.Any # any_of
| Gladius.Not # not_spec
| Gladius.Maybe # maybe
| Gladius.Ref # ref
| Gladius.ListOf # list_of
| Gladius.Cond # cond_spec
| Gladius.Schema # schema / open_schema
| Gladius.Default # default
| Gladius.Transform # transform
```
### `Gladius.Registry` API
```elixir
Gladius.Registry.register(name, spec) :: :ok
Gladius.Registry.unregister(name) :: :ok
Gladius.Registry.fetch!(name) :: conformable()
Gladius.Registry.registered?(name) :: boolean()
Gladius.Registry.all() :: %{atom => conformable()}
Gladius.Registry.clear() :: :ok # DANGER: global
Gladius.Registry.register_local(name, spec) :: :ok
Gladius.Registry.unregister_local(name) :: :ok
Gladius.Registry.clear_local() :: :ok
```
`fetch!/1` checks process-local overlay first, then global ETS.
### `Gladius.Coercions` API
```elixir
Gladius.Coercions.register({source, target}, fun) :: :ok
Gladius.Coercions.registered() :: %{{atom, atom} => function()}
Gladius.Coercions.lookup(source, target) :: function()
```
### Behavioural guarantees
1. `conform/2` is the single entry point. `valid?/2` and `explain/2` call it internally.
2. Specs are plain structs — store in variables, pass to functions, compose freely.
3. `all_of/1` pipelines shaped values through each spec in order.
4. `ref/1` is lazy — resolved at `conform/2` call time, not at spec build time.
5. Schema errors accumulate — `schema/1`, `open_schema/1`, `list_of/1` never short-circuit.
6. `default/2` fallbacks are never re-validated — injected as-is when a key is absent.
7. `transform/2` never runs on invalid data and never crashes the caller — exceptions become `%Error{predicate: :transform}`.
8. `conform/2` accepts structs transparently — `Map.from_struct/1` is applied automatically. Use `conform_struct/2` to re-wrap the output.
9. `defschema struct: true` — struct fields are inferred from schema keys at compile time via `Code.eval_quoted`.
10. `signature` is prod-safe — compiles away entirely in `:prod`.
11. Coercion registry is global and permanent — `Gladius.Coercions.register/2` uses `:persistent_term`. Call once at startup.
12. `gen/1` raises in `:prod`.
