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correct and clarify the rules about integer conversions.

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DELTA=15  (6 added, 1 deleted, 8 changed)
OCL=34549
CL=34564
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Rob Pike 2009-09-11 11:51:00 -07:00
parent 70eef675d5
commit 61dd8363ba
1 changed files with 14 additions and 9 deletions
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23
doc/go_spec.html
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@ -3890,22 +3890,27 @@ to a variable of type T.
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<li>
2) The conversion succeeds if the value would be assignment-compatible
to a variable of type T if the value type or T or any of their component
to a variable of type T if the value's type, or T, or any of their component
types are unnamed (§<a href="#Type_identity_and_compatibility">Type identity and compatibility</a>).
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<li>
3) Between integer types. If the value is a signed quantity, it is
3a) From an ideal number to an integer type.
The ideal number must be representable in the result type; it must not overflow.
For example, <code>uint8(0xFF)</code> is legal but <code>int8(0xFF)</code> is not.
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3b) From a non-ideal integer value to an integer type. 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 result type size.
For example, <code>uint32(int8(0xFF))</code> is <code>0xFFFFFFFF</code>.
The conversion always yields a valid value; there is no signal for overflow.
extended. It is then truncated to fit in the result type's size.
For example, if <code>x := uint16(0x10F0)</code>, then <code>uint32(int8(x)) == 0xFFFFFFF0</code>.
The conversion always yields a valid value; there is no indication of overflow.
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4) Between integer and floating point types, or between floating point
types. To avoid overdefining the properties of the conversion, for
now it is defined as a ``best effort'' conversion. The conversion
always succeeds but the value may be a NaN or other problematic
result. <font color=red>TODO: clarify?</font>
result. <font color=red>TODO: clarify</font>
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5) Strings permit three special conversions:
@ -3915,7 +3920,7 @@ result. <font color=red>TODO: clarify?</font>
representation of the integer.
<pre>
string(0x65e5) // "\u65e5"
string(0x65e5) // "\u65e5" == "日" == "\xe6\x97\xa5"
</pre>
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@ -3924,9 +3929,9 @@ string(0x65e5) // "\u65e5"
concatenation of the individual integers converted to strings.
If the slice value is <code>nil</code>, the result is the empty string.
<pre>
string([]int{0x65e5, 0x672c, 0x8a9e}) // "\u65e5\u672c\u8a9e"
</pre>
string([]int{0x65e5, 0x672c, 0x8a9e}) // "\u65e5\u672c\u8a9e" == "日本語"</pre>
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5c) Converting a slice of bytes yields a string whose successive
bytes are those of the slice. If the slice value is <code>nil</code>,