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Proposal: expression to create pointer to simple types

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Re: Proposal: expression to create pointer to simple types

#11

Post by fanf2 »

This reminds me a lot of C99 compound literals: one of the Go suggestions looks like &int(3) which in C99 is spelled &(int){ 3 }.

(I was slightly surprised when I learned that C99 compound literals are not just for structs: you can use any complete object type, and the result is an lvalue so you can take its address.)

Re: Proposal: expression to create pointer to simple types

#12

Post by not_knuth »

w-m wrote: post #3

How exemplary that he filled in the full template questionnaire for language changes, including questions such as "Would you consider yourself a novice, intermediate, or experienced Go programmer?" (he replied "I have some experience").

IIRC Tim Berners-Lee also rather amusingly called himself a "Web Developer" at a conference.

Re: Proposal: expression to create pointer to simple types

#13

Post by kevincox »

I was surprised that you can't apply & to any value. I thought it was gut an ordinary operator and it would ensure that the value it was applied to would be put onto the heap.

  s := S{}
  sp := &s // Works
  _ = sp
  
  _ = &S{} // Works
  
  i := int32(1)
  ip := &i // Works!
  _ = ip

  _ = &int32(1) // Doesn't work!
https://play.golang.org/p/fdgvbEwJWgh

It seems odd that you can't apply & to a function's return value. I think the best approach would be making & work in basically any scenario. For example the following also doesn't currently work.

  &(int32(1) + int32(1))
It seems like it should be possible to "desugar" &X to `_tmp = X; &_tmp` and solve this weirdness.

Re: Proposal: expression to create pointer to simple types

#14

Post by jerf »

the-dude wrote: post #2

Can I create a pointer to a pointer?

Yes, however the utility of doing so in Go is fairly limited. Go has "pointers" but doesn't have pointer arithmetic, and the big use case of pointer-to-pointer in C is to iterate over an array of pointers via pointer arithmetic. Personally I would call them "references" since I consider pointer arithmetic to be the thing that makes pointers pointers and not just references, but that's a personal opinion, not a universally-agreed-upon definition.

Re: Proposal: expression to create pointer to simple types

#16

Post by jerf »

kevincox wrote: post #13

I was surprised that you can't apply & to any value. I thought it was gut an ordinary operator and it would ensure that the value it was applied to would be put onto the heap. s := S{} sp := &s // Works _ = sp _ = &S{} // Works i := int32(1) ip := &i // Works! _ = ip _ = &int32(1) // Doesn't work! https://play.golang.org/p/fdgvbEwJWgh It seems odd that you can't apply & to a function's return value. I think the best…

One of the things I think the Go tutorials don't make a big enough deal of is that Go is relatively explicit about allocations. := isn't just a shortcut for declaring variables, it's an allocation, and an error to use it when it doesn't allocate. var X Sometype isn't just a declaration, it's an allocation.

:= kinda smears the clarity by not allocating if you have a variable on the left that is already allocated, and there's some other places where it kinda smears things up, but at the core, Go makes you explicitly allocate.

Re: Proposal: expression to create pointer to simple types

#17

Post by jerf »

darksaints wrote: post #15

For a language that has taken extreme measures to exclude generics because they are deemed to complex, this proposal is absolutely surprising to me. And I'm still not sure what practical benefit comes from it.

I'm not sure why this would be posted to HN, honestly; it's a very "inside baseball" thing. In my personal experience this would save a lot less than one line per module. I've encountered this, but it's infrequent. The benefit is very minimal in practice.

Re: Proposal: expression to create pointer to simple types

#18

Post by gowld »

not_knuth wrote: post #12
w-m wrote: post #3

How exemplary that he filled in the full template questionnaire for language changes, including questions such as "Would you consider yourself a novice, intermediate, or experienced Go programmer?" (he replied "I have some experience").

IIRC Tim Berners-Lee also rather amusingly called himself a "Web Developer" at a conference.

He did develop the web.

Re: Proposal: expression to create pointer to simple types

#20

Post by emodendroket »

darksaints wrote: post #15

For a language that has taken extreme measures to exclude generics because they are deemed to complex, this proposal is absolutely surprising to me. And I'm still not sure what practical benefit comes from it.

Imagine you want to create an instance of a struct with many string and int pointer fields. This is actually a big pain in the ass in Go (the AWS SDK offers an aws.String helper for this reason).
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