Define a type as a generic type instantiation

php Editor Xigua will introduce you to an important concept today - defining types as instantiations of generic types. In programming, generics are a flexible way to write general code without specifying a specific type. By defining a type as a generic type instantiation, we can specify the specific type when using it, making the code more flexible and reusable. Next, let’s dive into this concept and see how to implement generics in PHP.

Question content

In the following example, I try to define a PreciseAdder type to simplify the use of instantiated generic types. Unfortunately, the go compiler seems to think that methods defined on generic types are not applicable to PreciseAdder types. I know I can solve this problem through composition, but is there a way to solve this problem through type definition, and if not, what is the reason?

package main

type Addable interface {
    Add()
}

type Adder[T Addable] struct{}

func (a Adder[T]) DoAdd(){}

type PreciseAddable struct{}

func (p PreciseAddable)Add(){}

type PreciseAdder Adder[PreciseAddable]

func main() {
    var p PreciseAdder
    p.DoAdd()
}

Solution

This:

type PreciseAdder Adder[PreciseAddable]

is a type declaration, more specifically a type definition. It creates a new type, removing all methods.

Instead use a type alias that will preserve all methods, it just introduces a new identifier to reference the same type:

type PreciseAdder = Adder[PreciseAddable]

(Note the = symbol between the identifier and the type.)

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