Why Can't I Assign One Generic Type to Another in Go, Even If Their Type Arguments Are Compatible?

Understanding Generic Type Assignment Restrictions

In Go, a generic can't be assigned to another even if their type arguments can be due to the nature of generic instantiation.

Generic Types in Go

Generic types allow for code reuse by defining a template that can be used with different data types. When you instantiate a generic type, you provide concrete type arguments to specify the specific data type used.

Assignment Restrictions

Assigning a value of one generic type to another may not always be allowed. This is because instantiating a generic type with different type arguments results in two distinct named types.

For example:

type Props[G Generic] struct{}

type Example struct{}

func (Example) ID() string { return "" }

var ExampleProps = Props[Example]{}

func Problem() Props[Generic] {
    return ExampleProps // Compilation error
}

In this example, Example implements the Generic interface. However, Props[Example] and Props[Generic] are still considered different types. Therefore, assigning ExampleProps (which is of type Props[Example]) to Problem (which returns Props[Generic]) is not allowed.

Resolution

If you want to assign values between generic types, you can instantiate the generic type with a type parameter. For example:

func Problem[T Generic](v T) Props[T] {
    return Props[T]{Value: v}
}

In this case, Problem takes a generic parameter T and instantiates Props with T. This allows for more flexibility and can be used in situations where the type arguments meet specific conditions.

The above is the detailed content of Why Can't I Assign One Generic Type to Another in Go, Even If Their Type Arguments Are Compatible?. For more information, please follow other related articles on the PHP Chinese website!