Named type
Format: type typeName underlying-type
A constructor with underlying-type value will exist without declaring
package main
import (
"fmt"
)
// declare named type
// type name underlying-type
type C float64
type F float64
// declare constant by named type
const (
FreezingC C = 0
BoilingC C = 100
)
// convert from C to F
func CToF(c C) F {
return F(c*9/5 + 32)
}
func FToC(f F) C {
return C((f - 32) * 5 / 9)
}
func main() {
fmt.Printf("Freezing C:%g\n", FreezingC)
fmt.Printf("Freezing F:%g\n", CToF(FreezingC))
fmt.Printf("Boiling C:%g\n", BoilingC)
fmt.Printf("Boiling F:%g\n", CToF(BoilingC))
}
Declare convert function in named type
format: func (variableName NamedType) funcName() {...}
package main
import (
"fmt"
)
// declare named type
// type name underlying-type
type C float64
type F float64
// declare constant by named type
const (
FreezingC C = 0
BoilingC C = 100
)
// convert from C to F
func (c C) CToF() F {
return F(c*9/5 + 32)
}
func main() {
fmt.Printf("Freezing C:%g\n", FreezingC)
fmt.Printf("Freezing F:%g\n", FreezingC.CToF())
fmt.Printf("Boiling C:%g\n", BoilingC)
fmt.Printf("Boiling F:%g\n", BoilingC.CToF())
}
Comparasion
Named type can compare with underlying type.
Different named type can't be compared, will panic
package main
import (
"fmt"
)
// declare named type
// type name underlying-type
type C float64
type F float64
func main() {
fmt.Printf("%t\n", C(100) == C(100)) // true
fmt.Printf("%t\n", C(100) == 100) // true
// fmt.Printf("%t", C(100) == F(100)) // panic
}
panic
 |  |
Define String() method in named type, this method will be called directly
Format: func (Named type) funcName namedType {..}
package main
import (
"fmt"
)
// declare named type
// type name underlying-type
type C float64
type F float64
func (c C) String() string {
return fmt.Sprintf("%g-C", c)
}
func main() {
fmt.Printf("%s", C(23))
}
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