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# C++ concepts: Hash

From cppreference.com
< cpp‎ | concept

A `Hash` is a function object for which the output depends only on the input and has a very low probability of yielding the same output given different input values.

It must satisfy the requirements of `CopyConstructible` and `Destructible`.

Even if passed a lvalue, the Hash object must not modify the input.

Several calls with the same input shall return the same output.

The probability of h(a)==h(b) for a!=b should approach 1.0/std::numeric_limits<size_t>::max().

# Hash::operator()

std::size_t operator() ( const Key& k ) |  |

### [edit] Standard library

std::hash

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