typetraits

This module defines compile-time reflection procs for working with types.

Unstable API.

Procs

proc name(t: typedesc): string {...}{.magic: "TypeTrait".}

Returns the name of the given type.

Alias for system.`$`(t) since Nim v0.20.

  Source Edit
proc arity(t: typedesc): int {...}{.magic: "TypeTrait".}
Returns the arity of the given type. This is the number of "type" components or the number of generic parameters a given type t has.

Examples:

assert arity(seq[string]) == 1
assert arity(array[3, int]) == 2
assert arity((int, int, float, string)) == 4
  Source Edit
proc genericHead(t: typedesc): typedesc {...}{.magic: "TypeTrait".}

Accepts an instantiated generic type and returns its uninstantiated form.

For example:

  • seq[int].genericHead will be just seq
  • seq[int].genericHead[float] will be seq[float]

A compile-time error will be produced if the supplied type is not generic.

See also:

Example:

type
  Functor[A] = concept f
    type MatchedGenericType = genericHead(f.type)
      # `f` will be a value of a type such as `Option[T]`
      # `MatchedGenericType` will become the `Option` type
  Source Edit
proc stripGenericParams(t: typedesc): typedesc {...}{.magic: "TypeTrait".}
This trait is similar to genericHead, but instead of producing error for non-generic types, it will just return them unmodified.   Source Edit
proc supportsCopyMem(t: typedesc): bool {...}{.magic: "TypeTrait".}

This trait returns true iff the type t is safe to use for copyMem.

Other languages name a type like these blob.

  Source Edit
proc isNamedTuple(T: typedesc): bool {...}{.magic: "TypeTrait".}
Return true for named tuples, false for any other type.   Source Edit
proc distinctBase(T: typedesc): typedesc {...}{.magic: "TypeTrait".}
Returns base type for distinct types, works only for distinct types. compile time error otherwise   Source Edit
proc lenTuple(T: typedesc[tuple]): int {...}{.magic: "TypeTrait".}
Return number of elements of T   Source Edit

Macros

macro genericParams(T: typedesc): untyped
return tuple of generic params for generic T

Examples:

type
  Foo[T1, T2] = object
doAssert genericParams(Foo[float, string]) is (float, string)
  Source Edit

Templates

template lenTuple(t: tuple): int
Return number of elements of t   Source Edit
template get(T: typedesc[tuple]; i: static int): untyped
Return i`th element of `T   Source Edit

Exports

$, $, $, $, $, $, $, $, $, $, $, $, $, $, $, $, $, $