Type
std::meta::typ contains methods on the built-in Type type used for representing
a type in the source program.
Functions
pub comptime fn fresh_type_variable() -> Type {}
Creates and returns an unbound type variable. This is a special kind of type internal
to type checking which will type check with any other type. When it is type checked
against another type it will also be set to that type. For example, if a is a type
variable and we have the type equality (a, i32) = (u8, i32), the compiler will set
a equal to u8.
Unbound type variables will often be rendered as _ while printing them. Bound type
variables will appear as the type they are bound to.
This can be used in conjunction with functions which internally perform type checks
such as Type::implements or Type::get_trait_impl to potentially grab some of the types used.
Note that calling Type::implements or Type::get_trait_impl on a type variable will always
fail.
Example:
trait Serialize<let N: u32> {}
impl Serialize<1> for Field {}
impl<T, let N: u32, let M: u32> Serialize<N * M> for [T; N]
where T: Serialize<M> {}
impl<T, U, let N: u32, let M: u32> Serialize<N + M> for (T, U)
where T: Serialize<N>, U: Serialize<M> {}
Source code: test_programs/compile_success_empty/comptime_type/src/main.nr#L20-L30
let typevar1 = std::meta::typ::fresh_type_variable();
let constraint = quote { Serialize<$typevar1> }.as_trait_constraint();
let field_type = quote { Field }.as_type();
// Search for a trait impl (binding typevar1 to 1 when the impl is found):
assert(field_type.implements(constraint));
// typevar1 should be bound to the "1" generic now:
assert_eq(typevar1.as_constant().unwrap(), 1);
// If we want to do the same with a different type, we need to
// create a new type variable now that `typevar1` is bound
let typevar2 = std::meta::typ::fresh_type_variable();
let constraint = quote { Serialize<$typevar2> }.as_trait_constraint();
let array_type = quote { [(Field, Field); 5] }.as_type();
assert(array_type.implements(constraint));
// Now typevar2 should be bound to the serialized pair size 2 times the array length 5
assert_eq(typevar2.as_constant().unwrap(), 10);
Source code: test_programs/compile_success_empty/comptime_type/src/main.nr#L130-L150
Methods
as_array
comptime fn as_array(self) -> Option<(Type, Type)> {}
If this type is an array, return a pair of (element type, size type).
Example:
comptime {
let array_type = quote { [Field; 3] }.as_type();
let (field_type, three_type) = array_type.as_array().unwrap();
assert(field_type.is_field());
assert_eq(three_type.as_constant().unwrap(), 3);
}
as_constant
comptime fn as_constant(self) -> Option<u32> {}
If this type is a constant integer (such as the 3 in the array type [Field; 3]),
return the numeric constant.
as_integer
comptime fn as_integer(self) -> Option<(bool, u8)> {}
If this is an integer type, return a boolean which is true
if the type is signed, as well as the number of bits of this integer type.
as_slice
comptime fn as_slice(self) -> Option<Type> {}
If this is a slice type, return the element type of the slice.
as_str
comptime fn as_str(self) -> Option<Type> {}
If this is a str<N> type, returns the length N as a type.
as_struct
comptime fn as_struct(self) -> Option<(StructDefinition, [Type])> {}
If this is a struct type, returns the struct in addition to any generic arguments on this type.
as_tuple
comptime fn as_tuple(self) -> Option<[Type]> {}
If this is a tuple type, returns each element type of the tuple.
get_trait_impl
comptime fn get_trait_impl(self, constraint: TraitConstraint) -> Option<TraitImpl> {}
Retrieves the trait implementation that implements the given
trait constraint for this type. If the trait constraint is not
found, None is returned. Note that since the concrete trait implementation
for a trait constraint specified from a where clause is unknown,
this function will return None in these cases. If you only want to know
whether a type implements a trait, use implements instead.
Example:
comptime {
let field_type = quote { Field }.as_type();
let default = quote { Default }.as_trait_constraint();
let the_impl: TraitImpl = field_type.get_trait_impl(default).unwrap();
assert(the_impl.methods().len(), 1);
}
implements
comptime fn implements(self, constraint: TraitConstraint) -> bool {}
true if this type implements the given trait. Note that unlike
get_trait_impl this will also return true for any where constraints
in scope.
Example:
fn foo<T>() where T: Default {
comptime {
let field_type = quote { Field }.as_type();
let default = quote { Default }.as_trait_constraint();
assert(field_type.implements(default));
let t = quote { T }.as_type();
assert(t.implements(default));
}
}
is_bool
comptime fn is_bool(self) -> bool {}
true if this type is bool.
is_field
comptime fn is_field(self) -> bool {}
true if this type is Field.
Trait Implementations
impl Eq for Type
impl Hash for Type
Note that this is syntactic equality, this is not the same as whether two types will type check
to be the same type. Unless type inference or generics are being used however, users should not
typically have to worry about this distinction unless std::meta::typ::fresh_type_variable is used.