what’s type assertion in Go

tags: learning programming go

content

to check if a go type has an interface, we could do:
- could be struct or non-struct type, as long as it’s a type
- which means interface is also included!

value, ok := interface_var.(TypeName)

example:

var x any
x = 10
value, ok := x.(int)
fmt.Println(value, ok)  // 10, true
value, ok := x.(string)
fmt.Println(value, ok)  // "", false
 
str := x.(string)  // PANIC!

another example:

type MyType string
func checkType (a any) {
	b, ok := a.(MyType)
}

if a is the type of MyType, b gets the value and type of a
if a is a different type than MyType, b becomes zero value of MyType (MyType{})

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go-interface-basics-1

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