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- updated spec w/ respect to variable types and shift operators

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SVN=121774
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Robert Griesemer 2008-06-09 16:32:49 -07:00
parent a32063b00e
commit 4ff63a4794
1 changed files with 32 additions and 13 deletions
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45
doc/go_lang.txt
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@ -4,7 +4,7 @@ The Go Programming Language (DRAFT)
Robert Griesemer, Rob Pike, Ken Thompson
----
(June 6, 2008)
(June 9, 2008)
This document is a semi-informal specification/proposal for a new
systems programming language. The document is under active
@ -916,6 +916,8 @@ constant, variable, or function.
Declaration = ConstDecl | TypeDecl | VarDecl | FunctionDecl | ExportDecl .
TODO: specify range of visibility, scope rules.
Const declarations
----
@ -982,6 +984,18 @@ declaration the type of the initial value defines the type of the variable.
If the expression list is present, it must have the same number of elements
as there are variables in the variable specification.
If the variable type is omitted, an initialization expression (or expression
list) must be present, and the variable type is the type of the expression
value (in case of a list of variables, the variables assume the types of the
corresponding expression values).
If the variable type is omitted, and the corresponding initialization expression
is a constant expression of abstract int or floating point type, the type
of the variable is "int" or "float" respectively:
var i = 0 // i has int type
var f = 3.1415 // f has float type
The syntax
SimpleVarDecl = identifier ":=" Expression .
@ -994,12 +1008,12 @@ is shorthand for
f := func() int { return 7; }
ch := new(chan int);
Also, in some contexts such as if or for statements,
this construct can be used to
declare local temporary variables.
Also, in some contexts such as "if", "for", or "switch" statements,
this construct can be used to declare local temporary variables.
TODO: var a, b = 1, "x"; is permitted by grammar but not by current compiler
Function and method declarations
----
@ -1151,16 +1165,21 @@ and
(a / b) is "truncated towards zero".
There are no implicit type conversions except for
constants and literals. In particular, unsigned and signed integer
variables cannot be mixed in an expression without explicit conversion.
There are no implicit type conversions: Except for the shift operators
"<<" and ">>", both operands of a binary operator must have the same type.
In particular, unsigned and signed integer values cannot be mixed in an
expression without explicit conversion.
The shift operators implement arithmetic shifts for signed integers
and logical shifts for unsigned integers. The properties of negative
shift counts are undefined. Unary '^' corresponds to C '~' (bitwise
complement).
The shift operators shift the left operand by the shift count specified by the
right operand. They implement arithmetic shifts if the left operand is a signed
integer, and logical shifts if it is an unsigned integer. The shift count must
be an unsigned integer. There is no upper limit on the shift count. It is
as if the left operand is shifted "n" times by 1 for a shift count of "n".
There is no '->' operator. Given a pointer p to a struct, one writes
Unary "^" corresponds to C "~" (bitwise complement). There is no "~" operator
in Go.
There is no "->" operator. Given a pointer p to a struct, one writes
p.f
to access field f of the struct. Similarly, given an array or map
pointer, one writes
@ -1272,7 +1291,7 @@ These conversions are called ``simple conversions''.
TODO: if interfaces were explicitly pointers, this gets simpler.
convert(int, 3.14159);
convert(uint32, ~0);
convert(uint32, ^0);
convert(interface{}, new(S))
convert(*AStructType, interface_value)