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| -rw-r--r-- | doc/manual/type_rel.txt | 16 |
1 files changed, 16 insertions, 0 deletions
diff --git a/doc/manual/type_rel.txt b/doc/manual/type_rel.txt index 5b68f73aa..1a753d773 100644 --- a/doc/manual/type_rel.txt +++ b/doc/manual/type_rel.txt @@ -111,6 +111,20 @@ relation is extended to the types ``var``, ``ref``, ``ptr``: .. XXX nil is a special value! +Covariance +---------- + +Covariance in Nim can be introduced only though pointer-like types such +as ``ptr`` and ``ref``. Sequence, Array and OpenArray types, instantiated +with pointer-like types will be considered covariant if and only if they +are also immutable. The introduction of a ``var`` modifier or addional +``ptr`` or ``ref`` indirections would result in invariant treatment of +these types. + +``proc`` types are curently always invariant, but future version of Nim +may relax this rule. + + Convertible relation -------------------- A type ``a`` is **implicitly** convertible to type ``b`` iff the following @@ -119,6 +133,8 @@ algorithm returns true: .. code-block:: nim # XXX range types? proc isImplicitlyConvertible(a, b: PType): bool = + if isSubtype(a, b) or isCovariant(a, b): + return true case a.kind of int: result = b in {int8, int16, int32, int64, uint, uint8, uint16, uint32, uint64, float, float32, float64} |