Introspection

TypeContracts provides several functions to inspect what contracts and behaviors are registered at any point.

describe(T) — pretty-print a contract

Prints the full contract for T to stdout (or an io keyword argument):

abstract type AbstractShape end

@contract AbstractShape "A 2-D geometric shape." begin
    area(::Self)::Float64      => "area enclosed by the shape"
    perimeter(::Self)::Float64 => "length of the boundary"
    :optional
    name(::Self)::String       => "human-readable name"
end

@invariants AbstractShape begin
    "area is non-negative" => x -> area(x) >= 0
end

describe(AbstractShape)
# Interface contract for AbstractShape
# ────────────────────────────────────────
#   A 2-D geometric shape.
#
#   Mandatory methods:
#     • area(::Self) :: Float64 — area enclosed by the shape
#     • perimeter(::Self) :: Float64 — length of the boundary
#   Optional methods:
#     • name(::Self) :: String — human-readable name
#   Behavioral invariants:
#     • area is non-negative

To capture the output, pass an IOBuffer:

buf = IOBuffer()
describe(AbstractShape; io = buf)
text = String(take!(buf))

describe(T, Val(:all)) — supertype chain

Shows contracts from every ancestor of T that has a registered contract:

describe(Circle, Val(:all))
# Full interface contract for Circle
# ========================================
#
#   From AbstractShape:
#     area(::Self) :: Float64
#     perimeter(::Self) :: Float64
#     [optional] name(::Self) :: String
#     [invariant] area is non-negative

list_contract(T) — method specs for one type

Returns the Vector{MethodSpec} registered directly for T:

specs = list_contract(AbstractShape)
# 3-element Vector{MethodSpec}:
#   area(::Self) :: Float64
#   perimeter(::Self) :: Float64
#   [optional] name(::Self) :: String

Each MethodSpec exposes:

Field	Type	Meaning
f	Function	the function object
arg_types	Vector{Any}	argument types (Self, TypeParamRef, or concrete type)
return_type	Type	display return type (Any when unspecified or parametric)
return_type_spec	Union{Type, TypeParamRef}	used for actual return type checking
description	String	human-readable signature string
optional	Bool	whether this method is optional
doc	String	per-method prose ("" if none)

list_contract(T, Val(:all)) — full chain

Returns a Dict{Type, Vector{MethodSpec}} mapping each ancestor with a contract to its specs:

list_contract(Circle, Val(:all))
# Dict{Type, Vector{MethodSpec}} with 1 entry:
#   AbstractShape => [area(::Self) :: Float64, ...]

list_behaviors(T) — behavioral specs

Returns the Vector{BehaviorSpec} registered for T:

list_behaviors(AbstractShape)
# [BehaviorSpec("area is non-negative", ..., false)]

Each BehaviorSpec has:

Field	Type	Meaning
description	String	invariant description
predicate	Function	x -> Bool
optional	Bool	whether this invariant is optional

registered_contracts() and registered_behaviors()

Return all registered contracts and behaviors as dictionaries — useful for tooling, documentation generators, or diagnostic scripts. Intended for interactive/REPL use:

registered_contracts()
# Dict{Type, Vector{MethodSpec}} with all registered contracts

registered_behaviors()
# Dict{Type, Vector{BehaviorSpec}} with all registered behaviors