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// -*- C++ -*-
#ifndef WIBBLE_MAYBE_H
#define WIBBLE_MAYBE_H
namespace wibble {
/*
A Maybe type. Values of type Maybe< T > can be either Just T or
Nothing.
Maybe< int > foo;
foo = Maybe::Nothing();
// or
foo = Maybe::Just( 5 );
if ( !foo.nothing() ) {
int real = foo;
} else {
// we haven't got anythig in foo
}
Maybe takes a default value, which is normally T(). That is what you
get if you try to use Nothing as T.
*/
template <typename T>
struct Maybe {
bool nothing() { return m_nothing; }
T &value() { return m_value; }
Maybe( bool n, const T &v ) : m_nothing( n ), m_value( v ) {}
Maybe( const T &df = T() )
: m_nothing( true ), m_value( df ) {}
static Maybe Just( const T &t ) { return Maybe( false, t ); }
static Maybe Nothing( const T &df = T() ) {
return Maybe( true, df ); }
operator T() { return value(); }
protected:
bool m_nothing:1;
T m_value;
};
template<>
struct Maybe< void > {
Maybe() {}
static Maybe Just() { return Maybe(); }
static Maybe Nothing() { return Maybe(); }
};
}
#endif
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