Why my Golang defined method not implemented implicitily while String() does
In https://tour.golang.org/methods/11
It states Under the hood, interface values can be thought of as a tuple of a value and a concrete type
I define M as follows
script1
package main
import (
"fmt"
)
type I interface {
M() string
}
type T struct {
S string
w string
}
func (t T) M() string {
return "dddd"
}
func main() {
var i I
i = T{"Hello","eeee"}
fmt.Printf("(%v, %T)", i, i)
fmt.Println(i)
}
This prints out ({Hello eee}, main.T){Hello eee}
interface i has vaule {Hello eee} and type main.T
script2:
package main
import (
"fmt"
)
type I interface {
M() string
}
type T struct {
S string
w string
}
func (t T) M() string {
return "dddd"
}
func (t T) String() string {
return "ccccc"
}
func main() {
var i I
i = T{"Hello","eeee"}
fmt.Printf("(%v, %T)", i, i)
fmt.Println(i)
}
This prints out (ccccc, main.T)ccccc.
interface i has vaule ccccc and type main.T
Seems when i add String() as Stringer defined by the fmt package in script2. The String() is implemented implicitily,not sure why?
I thought in script2 i would have value "{Hello eee}" and type main.T
go asked Nov 21 at 0:02
Honord
12
add a comment |
In https://tour.golang.org/methods/11
It states Under the hood, interface values can be thought of as a tuple of a value and a concrete type
I define M as follows
script1
package main
import (
"fmt"
)
type I interface {
M() string
}
type T struct {
S string
w string
}
func (t T) M() string {
return "dddd"
}
func main() {
var i I
i = T{"Hello","eeee"}
fmt.Printf("(%v, %T)", i, i)
fmt.Println(i)
}
This prints out ({Hello eee}, main.T){Hello eee}
interface i has vaule {Hello eee} and type main.T
script2:
package main
import (
"fmt"
)
type I interface {
M() string
}
type T struct {
S string
w string
}
func (t T) M() string {
return "dddd"
}
func (t T) String() string {
return "ccccc"
}
func main() {
var i I
i = T{"Hello","eeee"}
fmt.Printf("(%v, %T)", i, i)
fmt.Println(i)
}
This prints out (ccccc, main.T)ccccc.
interface i has vaule ccccc and type main.T
Seems when i add String() as Stringer defined by the fmt package in script2. The String() is implemented implicitily,not sure why?
I thought in script2 i would have value "{Hello eee}" and type main.T
go asked Nov 21 at 0:02
Honord
12
2
I don't understand the question, butfmt.Stringeris used by thefmtpackage for printing values. See also the Tour of Go: Stringers.
– JimB
Nov 21 at 0:18
add a comment |
In https://tour.golang.org/methods/11
It states Under the hood, interface values can be thought of as a tuple of a value and a concrete type
I define M as follows
script1
package main
import (
"fmt"
)
type I interface {
M() string
}
type T struct {
S string
w string
}
func (t T) M() string {
return "dddd"
}
func main() {
var i I
i = T{"Hello","eeee"}
fmt.Printf("(%v, %T)", i, i)
fmt.Println(i)
}
This prints out ({Hello eee}, main.T){Hello eee}
interface i has vaule {Hello eee} and type main.T
script2:
package main
import (
"fmt"
)
type I interface {
M() string
}
type T struct {
S string
w string
}
func (t T) M() string {
return "dddd"
}
func (t T) String() string {
return "ccccc"
}
func main() {
var i I
i = T{"Hello","eeee"}
fmt.Printf("(%v, %T)", i, i)
fmt.Println(i)
}
This prints out (ccccc, main.T)ccccc.
interface i has vaule ccccc and type main.T
Seems when i add String() as Stringer defined by the fmt package in script2. The String() is implemented implicitily,not sure why?
I thought in script2 i would have value "{Hello eee}" and type main.T
go asked Nov 21 at 0:02
Honord
12
In https://tour.golang.org/methods/11
It states Under the hood, interface values can be thought of as a tuple of a value and a concrete type
I define M as follows
script1
package main
import (
"fmt"
)
type I interface {
M() string
}
type T struct {
S string
w string
}
func (t T) M() string {
return "dddd"
}
func main() {
var i I
i = T{"Hello","eeee"}
fmt.Printf("(%v, %T)", i, i)
fmt.Println(i)
}
This prints out ({Hello eee}, main.T){Hello eee}
interface i has vaule {Hello eee} and type main.T
script2:
package main
import (
"fmt"
)
type I interface {
M() string
}
type T struct {
S string
w string
}
func (t T) M() string {
return "dddd"
}
func (t T) String() string {
return "ccccc"
}
func main() {
var i I
i = T{"Hello","eeee"}
fmt.Printf("(%v, %T)", i, i)
fmt.Println(i)
}
This prints out (ccccc, main.T)ccccc.
interface i has vaule ccccc and type main.T
Seems when i add String() as Stringer defined by the fmt package in script2. The String() is implemented implicitily,not sure why?
I thought in script2 i would have value "{Hello eee}" and type main.T
go go asked Nov 21 at 0:02
Honord
12
asked Nov 21 at 0:02
Honord
12
edited Nov 21 at 21:11
asked Nov 21 at 0:02
Honord
12
asked Nov 21 at 0:02
Honord
12
asked Nov 21 at 0:02
Honord
12
12
2
I don't understand the question, butfmt.Stringeris used by thefmtpackage for printing values. See also the Tour of Go: Stringers.
– JimB
Nov 21 at 0:18
add a comment |
2
I don't understand the question, butfmt.Stringeris used by thefmtpackage for printing values. See also the Tour of Go: Stringers.
– JimB
Nov 21 at 0:18
2
2
I don't understand the question, but
fmt.Stringer is used by the fmt package for printing values. See also the Tour of Go: Stringers.– JimB
Nov 21 at 0:18
I don't understand the question, but
fmt.Stringer is used by the fmt package for printing values. See also the Tour of Go: Stringers.– JimB
Nov 21 at 0:18
add a comment |
2 Answers
2
active
oldest
votes
You should call fmt.Println(i.M()) ?
Why you want fmt call a function while its'n exist?
A Stringer is a type that can describe itself as a string. The fmt package (and many others) look for this interface to print values
answered Nov 21 at 1:34
KibGzr
1,466610
Thanks for your answer. I understand i.M() will return dddd. I expect script1 return dddd like script2 return ccccc .
– Honord
Nov 21 at 1:37
@HenryXie why do you expect that?
– zerkms
Nov 21 at 2:47
The fmt package (and many others) look for this String() first to print values.
– KibGzr
Nov 21 at 3:46
add a comment |
Refer: https://golang.org/pkg/fmt/#Stringer
Stringer is implemented by any value that has a String method, which
defines the “native” format for that value. The String method is used
to print values passed as an operand to any format that accepts a
string or to an unformatted printer such as Print.
In your case, in script1 you are just printing out the struct. In script2 you are providing what the builder should use when an unformatted print occurs which is a function that prints out "ccccc".
answered Nov 21 at 1:51
Prajval M
1,079317
add a comment |
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2 Answers
2
active
oldest
votes
2 Answers
2
active
oldest
votes
active
oldest
votes
active
oldest
votes
You should call fmt.Println(i.M()) ?
Why you want fmt call a function while its'n exist?
A Stringer is a type that can describe itself as a string. The fmt package (and many others) look for this interface to print values
answered Nov 21 at 1:34
KibGzr
1,466610
Thanks for your answer. I understand i.M() will return dddd. I expect script1 return dddd like script2 return ccccc .
– Honord
Nov 21 at 1:37
@HenryXie why do you expect that?
– zerkms
Nov 21 at 2:47
The fmt package (and many others) look for this String() first to print values.
– KibGzr
Nov 21 at 3:46
add a comment |
You should call fmt.Println(i.M()) ?
Why you want fmt call a function while its'n exist?
A Stringer is a type that can describe itself as a string. The fmt package (and many others) look for this interface to print values
answered Nov 21 at 1:34
KibGzr
1,466610
Thanks for your answer. I understand i.M() will return dddd. I expect script1 return dddd like script2 return ccccc .
– Honord
Nov 21 at 1:37
@HenryXie why do you expect that?
– zerkms
Nov 21 at 2:47
The fmt package (and many others) look for this String() first to print values.
– KibGzr
Nov 21 at 3:46
add a comment |
You should call fmt.Println(i.M()) ?
Why you want fmt call a function while its'n exist?
A Stringer is a type that can describe itself as a string. The fmt package (and many others) look for this interface to print values
answered Nov 21 at 1:34
KibGzr
1,466610
You should call fmt.Println(i.M()) ?
Why you want fmt call a function while its'n exist?
A Stringer is a type that can describe itself as a string. The fmt package (and many others) look for this interface to print values
answered Nov 21 at 1:34
KibGzr
1,466610
edited Nov 21 at 1:40
answered Nov 21 at 1:34
KibGzr
1,466610
answered Nov 21 at 1:34
KibGzr
1,466610
answered Nov 21 at 1:34
KibGzr
1,466610
1,466610
Thanks for your answer. I understand i.M() will return dddd. I expect script1 return dddd like script2 return ccccc .
– Honord
Nov 21 at 1:37
@HenryXie why do you expect that?
– zerkms
Nov 21 at 2:47
The fmt package (and many others) look for this String() first to print values.
– KibGzr
Nov 21 at 3:46
add a comment |
Thanks for your answer. I understand i.M() will return dddd. I expect script1 return dddd like script2 return ccccc .
– Honord
Nov 21 at 1:37
@HenryXie why do you expect that?
– zerkms
Nov 21 at 2:47
The fmt package (and many others) look for this String() first to print values.
– KibGzr
Nov 21 at 3:46
Thanks for your answer. I understand i.M() will return dddd. I expect script1 return dddd like script2 return ccccc .
– Honord
Nov 21 at 1:37
Thanks for your answer. I understand i.M() will return dddd. I expect script1 return dddd like script2 return ccccc .
– Honord
Nov 21 at 1:37
@HenryXie why do you expect that?
– zerkms
Nov 21 at 2:47
@HenryXie why do you expect that?
– zerkms
Nov 21 at 2:47
The fmt package (and many others) look for this String() first to print values.
– KibGzr
Nov 21 at 3:46
The fmt package (and many others) look for this String() first to print values.
– KibGzr
Nov 21 at 3:46
add a comment |
Refer: https://golang.org/pkg/fmt/#Stringer
Stringer is implemented by any value that has a String method, which
defines the “native” format for that value. The String method is used
to print values passed as an operand to any format that accepts a
string or to an unformatted printer such as Print.
In your case, in script1 you are just printing out the struct. In script2 you are providing what the builder should use when an unformatted print occurs which is a function that prints out "ccccc".
answered Nov 21 at 1:51
Prajval M
1,079317
add a comment |
Refer: https://golang.org/pkg/fmt/#Stringer
Stringer is implemented by any value that has a String method, which
defines the “native” format for that value. The String method is used
to print values passed as an operand to any format that accepts a
string or to an unformatted printer such as Print.
In your case, in script1 you are just printing out the struct. In script2 you are providing what the builder should use when an unformatted print occurs which is a function that prints out "ccccc".
answered Nov 21 at 1:51
Prajval M
1,079317
add a comment |
Refer: https://golang.org/pkg/fmt/#Stringer
Stringer is implemented by any value that has a String method, which
defines the “native” format for that value. The String method is used
to print values passed as an operand to any format that accepts a
string or to an unformatted printer such as Print.
In your case, in script1 you are just printing out the struct. In script2 you are providing what the builder should use when an unformatted print occurs which is a function that prints out "ccccc".
answered Nov 21 at 1:51
Prajval M
1,079317
Refer: https://golang.org/pkg/fmt/#Stringer
Stringer is implemented by any value that has a String method, which
defines the “native” format for that value. The String method is used
to print values passed as an operand to any format that accepts a
string or to an unformatted printer such as Print.
In your case, in script1 you are just printing out the struct. In script2 you are providing what the builder should use when an unformatted print occurs which is a function that prints out "ccccc".
answered Nov 21 at 1:51
Prajval M
1,079317
answered Nov 21 at 1:51
Prajval M
1,079317
answered Nov 21 at 1:51
Prajval M
1,079317
answered Nov 21 at 1:51
Prajval M
1,079317
1,079317
add a comment |
add a comment |
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2
I don't understand the question, but
fmt.Stringeris used by thefmtpackage for printing values. See also the Tour of Go: Stringers.– JimB
Nov 21 at 0:18