alias: Shortening a Long Name

alias

The alias keyword assigns aliases to existing names. alias is different from and unrelated to alias this.

Shortening a long name

As discussed previously, some names may become too long to be convenient. Let’s consider the following function:

Stack!(Point!double) randomPoints(size_t count) { 
    auto points = new Stack!(Point!double);
    // ...
}

Having to type Stack!(Point!double) explicitly in multiple places in the program has a number of drawbacks:

• Longer names can make the code harder to read.

• It is unnecessary to be reminded at every point that the type is the Stack data structure that contains objects of the double instantiations of the Point struct template.

• If the requirements of the program change and let’s say double needs to be changed to real, this change must be carried out in multiple places.

These drawbacks can be eliminated by giving a new name Point to Stack!(Point!double) using alias:

alias Points = Stack!(Point!double);

// ...

Points randomPoints(size_t count) { 
    auto points = new Points;
    // ...
}

It may make sense to go further and define two aliases, one taking advantage of the other:

alias PrecisePoint = Point!double; 
alias Points = Stack!PrecisePoint;

The syntax of alias is the following:

alias new_name = existing_name;

After that definition, the new name and the existing name become synonymous; they mean the same thing in the program.

You may encounter the older syntax of this feature in some programs:

// Use of old syntax is discouraged: 
alias existing_name new_name;

alias is also useful when shortening names that otherwise need to be spelled out along with their module names. Let’s assume that the name Queen appears in two separate modules: chess and palace. When both modules are imported, typing merely Queen would cause a compilation error: