[go-nuts] How to return a slice by value?

Slices are passed by value, but slices are very small, essentially just a
pointer to an underlying array. That pointer is the reference.

On Fri, Sep 21, 2012 at 4:02 PM, Meir wrote:

Arrays and structs are value types.

Slice is a value type BUT its backing array may be shared w/ other
slices. One can think about passing a slice as shallow copying.

type S []T

is like

type S struct{
len, cap int
elems *[X]T // where X, len, cap are set/change by make,
append, [a:b] etc.
}

-j

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On Fri, Sep 21, 2012 at 4:14 PM, Jan Mercl wrote:

s/X/cap/g

see also: http://research.swtch.com/godata

-j

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and this one: http://blog.golang.org/2011/01/go-slices-usage-and-internals.html

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In other words, *everything* in go is pass-by-value. You just need to know
what the nature of that value is (a copy of a pointer is a lot different
than a copy of what's pointed to).

Sounds like what you really want is a new copy of an existing slice, which
you could do with the make and copy builtins.
I might be reading to much from your question.

You probably want to pass larger structs by reference, it is just not
automagically done for you.
new(SomeType) returns a pointer/reference to a newly allocated struct, not
the struct itself for instance.

You can pass by reference with the same syntax as c mostly.

Just like Java! :P
http://javadude.com/articles/passbyvalue.htm

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Indeed. Thank you!
http://play.golang.org/p/KXepSqvxje

I believe slices work like the code below:

type slice struct {
start *uintptr
length int64
capacity int64
}
example := make([]byte, 0, 10) // slice{start:calloc(*10*), length:*0*,
capacity:*10*}

return example // return the VALUE slice{start:calloc(*10*), length:*0*,
capacity:*10*}

example2 := make([]byte, len(example), cap(example))
copy(example2, example)
return example2 // return the VALUE slice{start:calloc(*10*), length:*0*,
capacity:*10*} but its a new COPY

len and cap are typed int, not int64.
this structure is called SliceHeader in
package reflect.

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Okay. Thanks for the quick reply.