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simple unit test and better documentation for the user defined type classes

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Zahary Karadjov
2013-11-17 22:50:26 +02:00
parent 4cea15d274
commit a068aaed3c
8 changed files with 113 additions and 57 deletions
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31
doc/manual.txt
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@@ -3289,27 +3289,36 @@ Declarative type classes are written in the following form:
for value in c:
type(value) is T
The identifiers following the `generic` keyword are treated as variables of
the matched type and the body of the type class consists of arbitrary code that
must be valid under these circumstances.
Specifically, the type class will be matched if:
The type class will be matched if:
a) all of the expressions within the body can be compiled for the tested type
b) all statically evaluatable boolean expressions in the body must be true
Please note that the ``is`` operator allows you to easily verify the precise type
signatures of the required operations, but since type inference and default
parameters are still applied in the provided block, it's also possible to encode
usage protocols that doesn't reveal implementation details.
The identifiers following the `generic` keyword represent instances of the
currently matched type. These instances can act both as variables of the type,
when used in contexts, where a value is expected, and as the type itself, when
used in a contexts, where a type is expected.
Please note that the ``is`` operator allows you to easily verify the precise
type signatures of the required operations, but since type inference and
default parameters are still applied in the provided block, it's also possible
to encode usage protocols that doesn't reveal implementation details.
As a special rule providing further convenience when writing type classes, any
type value appearing in a callable expression will be treated as a variable of
the designated type for overload resolution purposes, unless the type value was
passed in its explicit ``typedesc[T]`` form:
.. code-block:: nimrod
type
OutputStream = generic S
write(var S, string)
Much like generics, the user defined type classes will be instantiated exactly
once for each tested type and any static code included within them will also be
executed once.
Return Type Inference
---------------------