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talk about short, int, long etc.

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specify allowed conversions.

SVN=117458
This commit is contained in:
Rob Pike 2008-05-01 20:59:31 -07:00
parent 76abea7c6d
commit 5e391cff2c
1 changed files with 47 additions and 9 deletions
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56
doc/go_lang.txt
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@ -296,8 +296,6 @@ and floating point types:
uint32 the set of all unsigned 32-bit integers
unit64 the set of all unsigned 64-bit integers
byte alias for uint8
int8 the set of all signed 8-bit integers, in 2's complement
int16 the set of all signed 16-bit integers, in 2's complement
int32 the set of all signed 32-bit integers, in 2's complement
@ -307,13 +305,26 @@ and floating point 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 4 basic types, uint, int, float, and double,
which are platform-specific. The bit width of these types corresponds to
the ``natural bit width'' for the respective types for the given
platform. For instance, int is usally the same as int32 on a 32-bit
architecture, or int64 on a 64-bit architecture. These types are by
definition platform-specific and should be used with the appropriate
caution.
Additionally, Go declares several platform-specific type aliases:
ushort, short, uint, int, ulong, long, float, and double. 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.
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.
Also, ``byte'' is an alias for uint8.
Finally, a type ptrint is 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.
Two reserved words, "true" and "false", represent the
corresponding boolean constant values.
@ -1290,6 +1301,33 @@ TODO: are there parameters to any conversions? go.y has oexpr_list as the
contents of a TypeName() conversion; i expected expr instead and that's what
the others have.
Only some conversions are permitted.
1) Between integer types. If the value is a signed quantity, it is
sign extended to implicit infinite precision; otherwise it is zero
extended. It is then truncated to fit in the destination type size.
For example, uint32(int8(0xFF)) is 0xFFFFFFFF. The conversion always
yields a valid value; for instance, there is no signal for overflow.
2) Between integer and floating point types, or between floating point
types. To avoid overdefining the properties of the conversion, for
now we define it as a ``best effort'' conversion. The conversion
always succeeds but the value may be a NaN or other problematic
result. TODO: clarify?
3) Conversions between interfaces and compatible interfaces and struct
pointers. Invalid conversions (that is, conversions between
incompatible types) yield nil values. TODO: is nil right here? Or
should incompatible conversions fail immediately?
4) Conversions between ``any'' values and arbitrary types. Invalid
conversions yield nil values. TODO: is nil right here? Or should
incompatible conversions fail immediately?
Note that there is no linguistic mechanism to convert between pointers
and integers. A library may be provided under restricted circumstances
to acccess this conversion in low-level code but it will not be available
in general.
The constant generator 'iota'
----