go-generics-tilde-2

more advanced usage of type constraints and tilde

tags: learning go programming

content

REMINDER

• ~ works on go-type-constraint

examples

• we can define a type constraint that contains methods!

type Number interface {
	~int64 | ~float64
}
type NumberStringer interface {
	Number
	fmt.Stringer
}

• define a generic function with NumberStringer type constraint:

func DescribeSum[T NumberStringer](a, b T) string {
	return fmt.Printf("%s + %s = %v", a, b, a + b)
}

• now to make some variables that could be passed in DescribeSum:
  • the variable has to satisfy:
    • Number: underlying type is int64 or float64
    • and fmt.Stringer: has a method String() string

type MyInt int64
func (m MyInt)String() string{
	return fmt.Sprintf("MyInt(%v)", m)
}

• now we can pass type MyInt to DescribeSum:

myInt1 := MyInt(1)
myInt2 := MyInt(2)
fmt.Println(DescribeSum(myInt1, myInt2))
// prints: "MyInt(1) + MyInt(2) = MyInt(3)"
// notice: the sum is also type `MyInt`

note

• fmt.Stringer is just an interface with String() method
• source code:

type Stringer interface {
	String() string
}

up

• go-generics-tilde

down

reference