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update tutorial for new slicing rules.

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Rob Pike 2009-04-15 20:53:07 -07:00
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1 changed files with 13 additions and 7 deletions
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20
doc/go_tutorial.txt
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@ -188,8 +188,12 @@ In Go, since arrays are values, it's meaningful (and useful) to talk
about pointers to arrays.
The size of the array is part of its type; however, one can declare
a <i>slice</i> variable, to which one can assign any array value
with the same element type. Slices look a lot like arrays but have
a <i>slice</i> variable, to which one can assign a pointer to
any array
with the same element type or - much more commonly - a <i>slice
expression</i> of the form "a[low : high]", representing
the subarray indexed by "low" through "high-1".
Slices look a lot like arrays but have
no explicit size ("[]" vs. "[10]") and they reference a segment of
an underlying, often anonymous, regular array. Multiple slices
can share data if they represent pieces of the same array;
@ -203,7 +207,8 @@ of an array stored within your structure, you should use a regular
array.
When passing an array to a function, you almost always want
to declare the formal parameter to be a slice. Go will automatically
to declare the formal parameter to be a slice. When you call
the function, take the address of the array and Go will automatically
create (efficiently) a slice reference and pass that.
Using slices one can write this function (from "sum.go"):
@ -217,16 +222,17 @@ and invoke it like this:
Note how the return type ("int") is defined for "sum()" by stating it
after the parameter list.
The expression "[3]int{1,2,3}" -- a type followed by a brace-bounded expression
-- is a constructor for a value, in this case an array of 3 "ints". We pass it
to "sum()" by (automatically) promoting it to a slice.
-- is a constructor for a value, in this case an array of 3 "ints". Putting an "&"
in front gives us the address of a unique instance of the value. We pass the
pointer to "sum()" by (automatically) promoting it to a slice.
If you are creating a regular array but want the compiler to count the
elements for you, use "..." as the array size:
s := sum([...]int{1,2,3});
s := sum(&[...]int{1,2,3});
In practice, though, unless you're meticulous about storage layout within a
data structure, a slice - using empty brackets - is all you need:
data structure, a slice itself - using empty brackets and no "&" - is all you need:
s := sum([]int{1,2,3});