type definition and type alias

tags: learning go programming diff-between

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in go, we have

type MyInt int    // type definition
type AliasInt = int  // type alias

type definition is a completely new type:
type alias is just an alias, it’s interchangeable with the original type

func MyFunc1(i MyInt) {}
func MyFunc2(i AliaseInt) {}
myInt := MyInt(1)
aliasInt := AliaseInt(1)
justInt := 1

For MyFunc1(MyInt), only* the exact same type works
- only with an asterisk, see below go-untyped-constant

MyFunc1(myInt)  // of course it works
MyFunc1(aliasInt)  // nope, doesn't work
MyFunc1(justInt)  // nope

but this one works!

type MyInt int
func MyFunc1(i MyInt) {}
MyFunc1(1)

for MyFunc2(), only MyInt doesn’t work!

MyFunc2(1)  // of course it works
MyFunc2(myInt)  // nope
MyFunc2(aliasInt)  // of course it works
MyFunc2(justInt)  // yes, because aliasInt is an alias for int

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go-named-type

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