Motivation

A type satisfies a regular concept if it matches the requirements defined by the concept. This is an implicit match, the creator of the type did not declare intent to make the type satisfy the concept. While this is often useful, in other cases, stating an implements-relation between the type and the concept in the source code to make the intention clear produces more readable and safer code: An explicit concept is only satisfied by a type if such an implements-relation exists.

Use

implements C, ExC: X

Defines implements-relations for an existing type and existing concepts: X implements concepts C and ExC.

explicit:
  type
    ExD = concept d
      d.x is float

Defines an explicit concept ExD.

implements ExD:
  type
    Xx = object
      x: float

    Y = object
      x: float

type
  Y2 = object
    x: float

echo(Y is ExD)   # -> true
echo(Y2 is ExD)  # -> false

Defines implements-relations for new types: Xx and Y implement concept ExD. Note that, despite the fact that it fulfills the requirement in the body of ExD, Y2 does not satisfy ExD because ExD is explicit and there is no implements-relation defined between the two.

The implements-relation between a type and a concept automatically extends to aliases of the two and to derivatives of the type, but not to distinct aliases of the two and to refinements of the concept.

For more details see the source files in the tests directory.