From ebf14c625dcd4b02bb4b6575bf8312ca1d8d1cc5 Mon Sep 17 00:00:00 2001 From: Robert Griesemer Date: Thu, 30 Oct 2008 14:50:23 -0700 Subject: [PATCH] - clarified section on numeric types: platform-dependent types are different from platform-independent types (not just aliases), except for byte, uint8 - added missing documentation of new(a, len, cap) - updated todo/issues lists DELTA=70 (24 added, 21 deleted, 25 changed) OCL=17920 CL=18174 --- doc/go_spec.txt | 87 +++++++++++++++++++++++++------------------------ 1 file changed, 45 insertions(+), 42 deletions(-) diff --git a/doc/go_spec.txt b/doc/go_spec.txt index 0e2f67fc580..8978434ddb6 100644 --- a/doc/go_spec.txt +++ b/doc/go_spec.txt @@ -4,7 +4,7 @@ The Go Programming Language Specification (DRAFT) Robert Griesemer, Rob Pike, Ken Thompson ---- -(October 24, 2008) +(October 28, 2008) This document is a semi-formal specification of the Go systems @@ -28,9 +28,7 @@ Timeline (9/5/08): Missing: [ ] partial export of structs, methods -[ ] syntax for var args [ ] range statement: to be defined more reasonably -[ ] reflection support [ ] packages of multiple files [ ] Helper syntax for composite types: allow names/indices for maps/arrays, remove need for type in elements of composites @@ -46,10 +44,10 @@ Todo's: Open issues: +[ ] semantics of type decl and where methods are attached [ ] convert should not be used for composite literals anymore, in fact, convert() should go away [ ] if statement: else syntax must be fixed -[ ] should we have a shorter list of alias types? (byte, int, uint, float) [ ] old-style export decls (still needed, but ideally should go away) [ ] new(arraytype, n1, n2): spec only talks about length, not capacity (should only use new(arraytype, n) - this will allow later @@ -73,7 +71,7 @@ Open issues: [ ] Conversions: can we say: "type T int; T(3.0)" ? We could allow converting structurally equivalent types into each other this way. May play together with "type T1 T2" where we give another type name to T2. -[ ] Is . import implemented? +[ ] Is . import implemented / do we still need it? [ ] Do we allow empty statements? If so, do we allow empty statements after a label? and if so, does a label followed by an empty statement (a semicolon) still denote a for loop that is following, and can break L be used inside it? @@ -87,9 +85,13 @@ Open issues: Decisions in need of integration into the doc: [ ] pair assignment is required to get map, and receive ok. +[ ] len() returns an int, new(array_type, n) n must be an int Closed: +[x] should we have a shorter list of alias types? (byte, int, uint, float) - done +[x] reflection support +[x] syntax for var args [x] Do composite literals create a new literal each time (gri thinks yes) (Russ is putting in a change to this effect, essentially) [x] comparison operators: can we compare interfaces? @@ -610,12 +612,12 @@ The following identifiers are predeclared: - all basic types: - bool, uint8, uint16, uint32, uint64, int8, int16, int32, int64, + bool, byte, uint8, uint16, uint32, uint64, int8, int16, int32, int64, float32, float64, float80, string -- and their alias types: +- a set of platform-specific convenience types: - byte, ushort, uint, ulong, short, int, long, float, double, ptrint + uint, int, float, uintptr - the predeclared constants: @@ -623,13 +625,7 @@ The following identifiers are predeclared: - the predeclared functions (note: this list is likely to change): - cap(), convert(), len(), new(), panic(), print(), typeof(), ... - - -TODO(gri) We should think hard about reducing the alias type list to: -byte, uint, int, float, ptrint (note that for instance the C++ style -guide is explicit about not using short, long, etc. because their sizes -are unknown in general). + cap(), convert(), len(), new(), panic(), panicln(), print(), println(), typeof(), ... Const declarations @@ -881,6 +877,10 @@ and strings. Arithmetic types ---- +The following list enumerates all platform-independent numeric types: + + byte same as uint8 (for convenience) + uint8 the set of all unsigned 8-bit integers uint16 the set of all unsigned 16-bit integers uint32 the set of all unsigned 32-bit integers @@ -895,35 +895,23 @@ Arithmetic types float64 the set of all valid IEEE-754 64-bit floating point numbers float80 the set of all valid IEEE-754 80-bit floating point numbers -Additionally, Go declares several platform-specific type aliases; the -bit width of these types is ``natural'' for the respective types for the -given platform. For instance, int is usually the same as int32 on a -32-bit architecture, or int64 on a 64-bit architecture. +Additionally, Go declares a set of platform-specific numeric types for +convenience: -The integer sizes are defined such that short is at least 16 bits, int -is at least 32 bits, and long is at least 64 bits (and ditto for the -unsigned equivalents). Also, the sizes are such that short <= int <= -long. Similarly, float is at least 32 bits, double is at least 64 -bits, and the sizes have float <= double. + uint at least 32 bits, at most the size of the largest uint type + int at least 32 bits, at most the size of the largest int type + float at least 32 bits, at most the size of the largest float type + uintptr smallest uint type large enough to store the uninterpreted + bits of a pointer value - byte alias for uint8 - ushort uint16 <= ushort <= uint - uint uint32 <= uint <= ulong - ulong uint64 <= ulong +For instance, int might have the same size as int32 on a 32-bit +architecture, or int64 on a 64-bit architecture. - short int16 <= short <= int - int int32 <= int <= long - long int64 <= long - - float float32 <= float <= double - double float64 <= double - -An arithmetic type ``ptrint'' is also defined. It is an unsigned -integer type that is the smallest natural integer type of the machine -large enough to store the uninterpreted bits of a pointer value. - -Generally, programmers should use these types rather than the explicitly -sized types to maximize portability. +Except for byte, which is an alias for uint8, all numeric types +are different from each other to avoid portability issues. Conversions +are required when different numeric types are mixed in an expression or assignment. +For instance, int32 and int are not the same type even though they may have +the same size on a particular platform. Booleans @@ -2724,7 +2712,7 @@ type-specific list of expressions. It allocates memory for a variable of type "T" and returns a pointer of type "*T" to that variable. The memory is initialized as described in the section on initial values. - new(type, [optional list of expressions]) + new(type [, optional list of expressions]) For instance @@ -2741,6 +2729,21 @@ buffered channels, and maps. c := new(chan int, 10); # a pointer to a channel with a buffer size of 10 m := new(map[string] int, 100); # a pointer to a map with initial space for 100 elements +For arrays, a third argument may be provided to specify the array capacity: + + bp := new([]byte, 0, 1024); # a pointer to an empty open array with capacity 1024 + + + Packages ----