Re: [go-nuts] How to cast a multi-value?
On Tuesday, 18 May 2021 at 21:09:18 UTC+1 Amnon wrote: > My understanding was that a string had a pointer and a length > Yes indeed - sorry my brain was disengaged :-) > -- You received this message because you are subscribed to the Google Groups "golang-nuts" group. To unsubscribe from this group and stop receiving emails from it, send an email to golang-nuts+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/golang-nuts/907c7dd7-54f7-4ec4-8cee-4263c114da24n%40googlegroups.com.
Re: [go-nuts] How to cast a multi-value?
Assigning string values to string values or byte[] to byte[] does not require additional memory allocation. But conversion between string and byte[] does so most of the time, because the underlying array of a string is immutable, versus the mutable of a byte[]. Encapsulating the type cast encapsulates exactly this potentially costly operation. Whether this has a negativ or positive impact on potential compiler optimisation in respect to the need of a copy in this special case, is hard to determine. Amnon schrieb am Dienstag, 18. Mai 2021 um 22:09:18 UTC+2: > My understanding was that a string had a pointer and a length, > whereas a slice had a pointer and a length and a capacity. > > https://golang.org/src/reflect/value.go?s=59515:59567#L1973 > > > On Tuesday, 18 May 2021 at 20:32:39 UTC+1 Brian Candler wrote: > >> Assigning a string value to another variable doesn't double the memory >> usage. >> >> A value of type string consists of a pointer, a length, and a capacity, >> and only these are copied - so you get another copy of the pointer, >> pointing to the same data buffer. >> >>> -- You received this message because you are subscribed to the Google Groups "golang-nuts" group. To unsubscribe from this group and stop receiving emails from it, send an email to golang-nuts+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/golang-nuts/188a70df-4dff-40d7-a2d2-4ea64902aa28n%40googlegroups.com.
Re: [go-nuts] How to cast a multi-value?
My understanding was that a string had a pointer and a length, whereas a slice had a pointer and a length and a capacity. https://golang.org/src/reflect/value.go?s=59515:59567#L1973 On Tuesday, 18 May 2021 at 20:32:39 UTC+1 Brian Candler wrote: > Assigning a string value to another variable doesn't double the memory > usage. > > A value of type string consists of a pointer, a length, and a capacity, > and only these are copied - so you get another copy of the pointer, > pointing to the same data buffer. > >> -- You received this message because you are subscribed to the Google Groups "golang-nuts" group. To unsubscribe from this group and stop receiving emails from it, send an email to golang-nuts+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/golang-nuts/951b1505-e6d7-42d0-b78e-cea207956281n%40googlegroups.com.
Re: [go-nuts] How to cast a multi-value?
Assigning a string value to another variable doesn't double the memory usage. A value of type string consists of a pointer, a length, and a capacity, and only these are copied - so you get another copy of the pointer, pointing to the same data buffer. > -- You received this message because you are subscribed to the Google Groups "golang-nuts" group. To unsubscribe from this group and stop receiving emails from it, send an email to golang-nuts+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/golang-nuts/4c6168df-c5f3-44cd-8191-e6ed4672cbben%40googlegroups.com.
Re: [go-nuts] How to cast a multi-value?
'Keith Randall' via golang-nuts schrieb am
Di., 18. Mai 2021, 18:25:
> You can use a function call to do the cast:
>
> func byteErr2stringErr(b []byte, e error) (string, error) {
> return string(b), e
> }
> content, err := byteErr2stringErr(os.ReadFile(path))
>
> It's still using additional variables, but they are hidden inside the
> helper function.
> On Sunday, May 16, 2021 at 8:07:24 PM UTC-7 Kurtis Rader wrote:
>
>> On Sun, May 16, 2021 at 7:49 PM 'Marc Michael' via golang-nuts <
>> golan...@googlegroups.com> wrote:
>>
>>> as Go provides multi values I would expect that's possible to cast such
>>> a multi value. Do I see it correctly, that Go does not provide it?
>>>
>>> Example:
>>>
>>> os.ReadFile returns []byte, error.
>>> I want to cast the []byte to a string.
>>>
>>> content, err := os.ReadFile(path)
>>>
>>> Is it possible to cast the []byte directly to a string without using a
>>> second variable?
>>>
>>
>> No, it is not possible to transform the type of one return value in a
>> multi-valued
>> expression such as a function call. Such syntactic sugar would have limited
>> usefulness and, in my opinion, is likely to decrease readability and thus
>> be a source of bugs. If you find yourself needing to perform such
>> conversions so often that such a feature is useful that suggests the APIs
>> you're using need to be changed.
>>
>
Hello,
thanks for the clarification. I have thought that I had something overseen.
I have thought about introducing a second variable of type string, but this
would lead to doubling of the memory usage, especaly as I don't now really
how much data there is. With the additional function I think this would not
a real problem, as the []byte would go away if the additional function
finishes.
Thanks all for your help. :-)
Kindly regards
>
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Re: [go-nuts] How to cast a multi-value?
You can use a function call to do the cast:
func byteErr2stringErr(b []byte, e error) (string, error) {
return string(b), e
}
content, err := byteErr2stringErr(os.ReadFile(path))
It's still using additional variables, but they are hidden inside the
helper function.
On Sunday, May 16, 2021 at 8:07:24 PM UTC-7 Kurtis Rader wrote:
> On Sun, May 16, 2021 at 7:49 PM 'Marc Michael' via golang-nuts <
> golan...@googlegroups.com> wrote:
>
>> as Go provides multi values I would expect that's possible to cast such a
>> multi value. Do I see it correctly, that Go does not provide it?
>>
>> Example:
>>
>> os.ReadFile returns []byte, error.
>> I want to cast the []byte to a string.
>>
>> content, err := os.ReadFile(path)
>>
>> Is it possible to cast the []byte directly to a string without using a
>> second variable?
>>
>
> No, it is not possible to transform the type of one return value in a
> multi-valued
> expression such as a function call. Such syntactic sugar would have limited
> usefulness and, in my opinion, is likely to decrease readability and thus
> be a source of bugs. If you find yourself needing to perform such
> conversions so often that such a feature is useful that suggests the APIs
> you're using need to be changed.
>
> --
> Kurtis Rader
> Caretaker of the exceptional canines Junior and Hank
>
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Re: [go-nuts] How to cast a multi-value?
On Sun, May 16, 2021 at 7:49 PM 'Marc Michael' via golang-nuts < golang-nuts@googlegroups.com> wrote: > as Go provides multi values I would expect that's possible to cast such a > multi value. Do I see it correctly, that Go does not provide it? > > Example: > > os.ReadFile returns []byte, error. > I want to cast the []byte to a string. > > content, err := os.ReadFile(path) > > Is it possible to cast the []byte directly to a string without using a > second variable? > No, it is not possible to transform the type of one return value in a multi-valued expression such as a function call. Such syntactic sugar would have limited usefulness and, in my opinion, is likely to decrease readability and thus be a source of bugs. If you find yourself needing to perform such conversions so often that such a feature is useful that suggests the APIs you're using need to be changed. -- Kurtis Rader Caretaker of the exceptional canines Junior and Hank -- You received this message because you are subscribed to the Google Groups "golang-nuts" group. To unsubscribe from this group and stop receiving emails from it, send an email to golang-nuts+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/golang-nuts/CABx2%3DD9m0H-boFwAsGXu5wefwqS7cS6mDEZYbvOB99%2BCEqGHwA%40mail.gmail.com.
[go-nuts] How to cast a multi-value?
Hello, as Go provides multi values I would expect that's possible to cast such a multi value. Do I see it correctly, that Go does not provide it? Example: os.ReadFile returns []byte, error. I want to cast the []byte to a string. content, err := os.ReadFile(path) Is it possible to cast the []byte directly to a string without using a second variable? Kindly regards -- You received this message because you are subscribed to the Google Groups "golang-nuts" group. To unsubscribe from this group and stop receiving emails from it, send an email to golang-nuts+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/golang-nuts/CAEOc3dWn%3Dn%3DFNaQVhnu56yu9yaoVeJRin_m%2B7DNh8hvqV7Ck%2Bw%40mail.gmail.com.
