libsigc++: Lambdas

libsigc++ 2.2.11

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Lambdas

libsigc++ ships with basic lambda functionality and the sigc::group adaptor, which uses lambdas to transform a functor's parameter list. More...

## Modules
| group()
| sigc::group() alters an arbitrary functor by rebuilding its arguments from one or more lambda expressions.

## Classes
struct | sigc::lambda_base
| A hint to the compiler. More...
struct | sigc::lambda< T_type >
| Lambda type. More...

## Detailed Description

libsigc++ ships with basic lambda functionality and the sigc::group adaptor, which uses lambdas to transform a functor's parameter list.

The lambda selectors sigc::_1, sigc::_2, ..., sigc::_9 are used to select the first, second, ..., nineth argument from a list.

Examples:
  std::cout << sigc::_1(10,20,30); // returns 10
  std::cout << sigc::_2(10,20,30); // returns 20

Operators are defined so that, for example, lambda selectors can be used as placeholders in arithmetic expressions.

Examples:
  std::cout << (sigc::_1 + 5)(3); // returns (3 + 5)
  std::cout << (sigc::_1 * sigc::_2)(7,10); // returns (7 * 10)

If your compiler supports C++11 lambda expressions, they are often a good alternative to libsigc++'s lambda expressions. The following examples are equivalent to the previous ones.

[] (int x, int, int) -> int { return x; }(10,20,30); // returns 10
[] (int, int y, int) -> int { return y; }(10,20,30); // returns 20
[] (int x) -> int { return x + 5; }(3); // returns (3 + 5)
[] (int x, int y) -> int { return x * y; }(7,10); // returns (7 * 10)