bslh_hashpair

Detailed Description

Outline

• Purpose
• Description
  • Usage
    • Example 1: Hashing a Pair of Integer Values

Purpose

Provide hashAppend for std::pair.

Description

This component provides a free function template, bslh::hashAppend, overloaded for the std::pair class template. Including this function allows for std::pair types (and types that contain them) to be used as keys in BDE hashed containers.

Usage

This section illustrates intended usage of this component.

Example 1: Hashing a Pair of Integer Values

Suppose one must compute has that combines the hashes of several integer values, each of a different type:

char  c = 'a';
short s = static_cast<short>(1);

First, we can make that calculation by repeated invocations of a 'bslh::DefaultHashAlogorithm object:

bslh::DefaultHashAlgorithm hasherS;
hasherS(&c, sizeof(char));
hasherS(&s, sizeof(short));
 
bslh::DefaultHashAlgorithm::result_type hashS = hasherS.computeHash();

Now, the same calculation can also be be made if those same values are contained in a single std::pair object.

std::pair<char, short> t = std::make_pair(c, s);
 
bslh::DefaultHashAlgorithm hasherT;
bslh::hashAppend(hasherT, t);
 
bslh::DefaultHashAlgorithm::result_type hashT = hasherT.computeHash();

Finally, we confirm that we computed the same result.

assert(hashS == hashT);