Template Instantiation and Template Specializations

Template instantiation

Automatic code generation for a specific set of template parameter values is called an instantiation of that template for that specific set of parameter values. For example, to!string and to!int are two different instantiations of the to function template.

As we will mention again in a separate section below, distinct instantiations of templates produce distinct and incompatible types.

Template specializations

Although the getResponse() function template can, in theory, be used for any template type, the code that the compiler generates may not be suitable for every type. Let’s assume that we have the following type that represents points on a two-dimensional space:

struct Point {
    int x;
    int y; 
}

Although the instantiation of getResponse() for the Point type itself would be fine, the generated readf() call for Point cannot be compiled. This is because the standard library function readf() does not know how to read a Point object. The two lines that actually read the response would look like the the Point instantiation of the getResponse() function template below: