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| -rw-r--r-- | doc/manual.rst | 1 | ||||
| -rw-r--r-- | doc/sets_fragment.txt | 37 |
2 files changed, 35 insertions, 3 deletions
diff --git a/doc/manual.rst b/doc/manual.rst index d4d2aae91..d7d50d2aa 100644 --- a/doc/manual.rst +++ b/doc/manual.rst @@ -1126,6 +1126,7 @@ as ``MyEnum.value``: echo amb # Error: Unclear whether it's MyEnum.amb or OtherEnum.amb echo MyEnum.amb # OK. +To implement bit fields with enums see `Bit fields <#set-type-bit-fields>`_ String type ----------- diff --git a/doc/sets_fragment.txt b/doc/sets_fragment.txt index 7e53f15f1..e9cb4fa90 100644 --- a/doc/sets_fragment.txt +++ b/doc/sets_fragment.txt @@ -49,6 +49,37 @@ operation meaning ``excl(A, elem)`` same as ``A = A - {elem}`` ================== ======================================================== -Sets are often used to define a type for the *flags* of a procedure. This is -a much cleaner (and type safe) solution than just defining integer -constants that should be ``or``'ed together. +Bit fields +~~~~~~~~~~ + +Sets are often used to define a type for the *flags* of a procedure. +This is a cleaner (and type safe) solution than defining integer +constants that have to be ``or``'ed together. + +Enum, sets and casting can be used together as in: + +.. code-block:: nim + + type + MyFlag* {.size: sizeof(cint).} = enum + A + B + C + D + MyFlags = set[MyFlag] + + proc toNum(f: MyFlags): int = cast[cint](f) + proc toFlags(v: int): MyFlags = cast[MyFlags](v) + + assert toNum({}) == 0 + assert toNum({A}) == 1 + assert toNum({D}) == 8 + assert toNum({A, C}) == 5 + assert toFlags(0) == {} + assert toFlags(7) == {A, B, C} + +Note how the set turns enum values into powers of 2. + +For interoperability with C see the `bitsize pragma <#implementation-specific-pragmas-bitsize-pragma>`_ instead. + +If using enums and sets with C, use distinct cint. |