117 lines
4 KiB
C
117 lines
4 KiB
C
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/////////////////////////////////////////////////////////////////////////////
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// Name: wx/private/flagscheck.h
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// Purpose: helpers for checking that (bit)flags don't overlap
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// Author: Vaclav Slavik
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// Created: 2008-02-21
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// Copyright: (c) 2008 Vaclav Slavik
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// Licence: wxWindows licence
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/////////////////////////////////////////////////////////////////////////////
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#ifndef _WX_PRIVATE_FLAGSCHECK_H_
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#define _WX_PRIVATE_FLAGSCHECK_H_
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#include "wx/debug.h"
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// IBM xlC 8 can't parse the template syntax
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#if !defined(__IBMCPP__)
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#include "wx/meta/if.h"
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namespace wxPrivate
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{
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// These templates are used to implement wxADD_FLAG macro below.
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//
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// The idea is that we want to trigger *compilation* error if the flags
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// overlap, not just runtime assert failure. We can't implement the check
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// using just a simple logical operation, we need checks equivalent to this
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// code:
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//
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// mask = wxFLAG_1;
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// assert( (mask & wxFLAG_2) == 0 ); // no overlap
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// mask |= wxFLAG_3;
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// assert( (mask & wxFLAG_3) == 0 ); // no overlap
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// mask |= wxFLAG_3;
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// ...
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//
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// This can be done at compilation time by using templates metaprogramming
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// technique that makes the compiler carry on the computation.
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//
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// NB: If any of this doesn't compile with your compiler and would be too
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// hard to make work, it's probably best to disable this code and replace
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// the macros below with empty stubs, this isn't anything critical.
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template<int val> struct FlagsHaveConflictingValues
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{
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// no value here - triggers compilation error
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};
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template<int val> struct FlagValue
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{
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enum { value = val };
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};
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// This template adds its template parameter integer 'add' to another integer
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// 'all' and produces their OR-combination (all | add). The result is "stored"
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// as constant SafelyAddToMask<>::value. Combination of many flags is achieved
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// by chaining parameter lists: the 'add' parameter is value member of
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// another (different) SafelyAddToMask<> instantiation.
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template<int all, int add> struct SafelyAddToMask
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{
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// This typedefs ensures that no flags in the list conflict. If there's
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// any overlap between the already constructed part of the mask ('all')
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// and the value being added to it ('add'), the test that is wxIf<>'s
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// first parameter will be non-zero and so Added value will be
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// FlagsHaveConflictingValues<add>. The next statement will try to use
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// AddedValue::value, but there's no such thing in
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// FlagsHaveConflictingValues<> and so compilation will fail.
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typedef typename wxIf<(all & add) == 0,
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FlagValue<add>,
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FlagsHaveConflictingValues<add> >::value
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AddedValue;
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enum { value = all | AddedValue::value };
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};
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} // wxPrivate namespace
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// This macro is used to ensure that no two flags that can be combined in
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// the same integer value have overlapping bits. This is sometimes not entirely
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// trivial to ensure, for example in wxWindow styles or flags for wxSizerItem
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// that span several enums, some of them used for multiple purposes.
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//
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// By constructing allowed flags mask using wxADD_FLAG macro and then using
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// this mask to check flags passed as arguments, you can ensure that
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//
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// a) if any of the allowed flags overlap, you will get compilation error
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// b) if invalid flag is used, there will be an assert at runtime
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//
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// Example usage:
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//
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// static const int SIZER_FLAGS_MASK =
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// wxADD_FLAG(wxCENTRE,
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// wxADD_FLAG(wxHORIZONTAL,
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// wxADD_FLAG(wxVERTICAL,
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// ...
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// 0))...);
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//
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// And wherever flags are used:
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//
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// wxASSERT_VALID_FLAG( m_flag, SIZER_FLAGS_MASK );
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#define wxADD_FLAG(f, others) \
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::wxPrivate::SafelyAddToMask<f, others>::value
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#else
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#define wxADD_FLAG(f, others) (f | others)
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#endif
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// Checks if flags value 'f' is within the mask of allowed values
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#define wxASSERT_VALID_FLAGS(f, mask) \
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wxASSERT_MSG( (f & mask) == f, \
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"invalid flag: not within " #mask )
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#endif // _WX_PRIVATE_FLAGSCHECK_H_
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