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slices and string/array concatenation

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OCL=13382
CL=13382
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Rob Pike 2008-07-23 11:22:30 -07:00
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1 changed files with 44 additions and 6 deletions
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50
doc/go_lang.txt
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@ -4,7 +4,7 @@ The Go Programming Language (DRAFT)
Robert Griesemer, Rob Pike, Ken Thompson
----
(July 21, 2008)
(July 22, 2008)
This document is a semi-formal specification/proposal for a new
systems programming language. The document is under active
@ -1226,15 +1226,17 @@ Expression syntax is based on that of C but with fewer precedence levels.
PrimaryExpr =
identifier | Literal | "(" Expression ")" | "iota" |
Call | Conversion | Allocation |
Expression "[" Expression [ ":" Expression ] "]" | Expression "." identifier |
Expression "." "(" Type ")" .
Call | Conversion | Allocation | Index |
Expression "." identifier | Expression "." "(" Type ")" .
Call = Expression "(" [ ExpressionList ] ")" .
Conversion = "convert" "(" Type [ "," ExpressionList ] ")" |
ConversionType "(" [ ExpressionList ] ")" .
ConversionType = TypeName | ArrayType | MapType | StructType | InterfaceType .
Allocation = "new" "(" Type [ "," ExpressionList ] ")" .
Index = SimpleIndex | Slice .
SimpleIndex = Expression "[" Expression"]" .
Slice = Expression "[" Expression ":" Expression "]" .
binary_op = log_op | comm_op | rel_op | add_op | mul_op .
log_op = "||" | "&&" .
@ -1497,6 +1499,42 @@ to acccess this conversion in low-level code but it will not be available
in general.
Slices and array concatenation
----
Strings and arrays can be ``sliced'' to construct substrings or subarrays.
The index expressions in the slice select which elements appear in the
result. The result has indexes starting at 0 and length equal to the difference
in the index values in the slice. After
a := []int(1,2,3,4)
slice := a[1:3]
The array ``slice'' has length two and elements
slice[0] == 2
slice[1] == 3
The index values in the slice must be in bounds for the original
array (or string) and the slice length must be non-negative.
Slices are new arrays (or strings) storing copies of the elements, so
changes to the elements of the slice do not affect the original.
In the example, a subsequent assignment to element 0,
slice[0] = 5
would have no effect on ``a''.
Strings and arrays can also be concatenated using the ``+'' (or ``+='')
operator.
a += []int(5, 6, 7)
s := "hi" + string(c)
Like slices, addition creates a new array or string by copying the
elements.
The constant generator 'iota'
----
@ -2109,7 +2147,7 @@ followed by a series of declarations.
Program = PackageClause { ImportDecl [ ";" ] } { Declaration [ ";" ] } .
Initialization and Program Execution
Initialization and program execution
----
A package with no imports is initialized by assigning initial values to