...one of the most highly
regarded and expertly designed C++ library projects in the
world.
— Herb Sutter and Andrei
Alexandrescu, C++
Coding Standards
Return true if ch is in the character set.
constexpr bool
operator()(
unsigned char ch) const;
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Return true if ch is in the character set.
constexpr bool
operator()(
char ch) const;
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