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Diffstat (limited to 'doc/go_spec.html')
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1 files changed, 68 insertions, 73 deletions
diff --git a/doc/go_spec.html b/doc/go_spec.html index db149a9b5..5cd890ab9 100644 --- a/doc/go_spec.html +++ b/doc/go_spec.html @@ -1,9 +1,8 @@ <!-- title The Go Programming Language Specification --> -<!-- subtitle Version of May 26, 2010 --> +<!-- subtitle Version of June 1, 2010 --> <!-- -Todo -[ ] clarify: two equal lower-case identifiers from different packages denote different objects +TODO [ ] need language about function/method calls and parameter passing rules [ ] last paragraph of #Assignments (constant promotion) should be elsewhere and mention assignment to empty interface. @@ -17,6 +16,7 @@ Todo though obvious [ ] specify iteration direction for range clause [ ] review language on implicit dereferencing +[ ] clarify what it means for two functions to be "the same" when comparing them --> @@ -1121,9 +1121,9 @@ KeyType = Type . <p> The comparison operators <code>==</code> and <code>!=</code> -(§<a href="#Comparison_operators">Comparison operators</a>) must be fully defined for operands of the -key type; thus the key type must be a boolean, numeric, string, pointer, function, interface, -map, or channel type. If the key type is an interface type, these +(§<a href="#Comparison_operators">Comparison operators</a>) must be fully defined +for operands of the key type; thus the key type must not be a struct, array or slice. +If the key type is an interface type, these comparison operators must be defined for the dynamic key values; failure will cause a <a href="#Run_time_panics">run-time panic</a>. @@ -1374,58 +1374,6 @@ represents the <a href="#The_zero_value">zero value</a> for that type. Any value may be assigned to the <a href="#Blank_identifier">blank identifier</a>. </p> -<h3 id="Comparison_compatibility">Comparison compatibility</h3> - -<p> -Except as noted, values of any type may be compared to other values of -<a href="#Type_compatibility">compatible static type</a>. -Values of integer, floating-point, and string type may be compared using the -full range of <a href="#Comparison_operators;">comparison operators</a>; -booleans and complex values may be compared only for equality or inequality. -</p> - -<p> -Values of composite type may be -compared for equality or inequality using the <code>==</code> and -<code>!=</code> operators, with the following provisos: -</p> -<ul> -<li> -Arrays and structs may not be compared to anything. -</li> -<li> -A slice value may only be compared explicitly against <code>nil</code>. -A slice value is equal to <code>nil</code> if it has been assigned the explicit -value <code>nil</code>, if it is uninitialized, or if it has -been assigned another slice value equal to <code>nil</code>· -</li> -<li> -An interface value is equal to <code>nil</code> if it has -been assigned the explicit value <code>nil</code>, if it is uninitialized, -or if it has been assigned another interface value equal to <code>nil</code>. -</li> -<li> -For types that can be compared to <code>nil</code>, -two values of the same type are equal if they both equal <code>nil</code>, -unequal if one equals <code>nil</code> and one does not. -</li> -<li> -Pointer values are equal if they point to the same location. -</li> -<li> -Function values are equal if they refer to the same function. -</li> -<li> -Channel and map values are equal if they were created by the same call to <code>make</code> -(§<a href="#Making_slices">Making slices</a>, maps, and channels). -When comparing two values of channel type, the channel value types -must be identical but the channel direction is ignored. -</li> -<li> -Interface values may be compared if they have compatible static types. -They will be equal only if they have the same dynamic type and the underlying values are equal. -</li> -</ul> <h2 id="Blocks">Blocks</h2> @@ -2960,11 +2908,7 @@ not occur. For instance, it may not assume that <code>x < x + 1</code> is alw <h3 id="Comparison_operators">Comparison operators</h3> <p> -Comparison operators yield a value of type <code>bool</code>. -The operators <code>==</code> and <code>!=</code> apply -to operands of all types except arrays and structs. -All other comparison operators apply only to integer, floating-point -and string values. +Comparison operators compare two operands and yield a value of type <code>bool</code>. </p> <pre class="grammar"> @@ -2977,20 +2921,71 @@ and string values. </pre> <p> -Operands of numeric type are compared in the usual way. -</p> -<p> -Operands of string type are compared byte-wise (lexically). -</p> +The operands must be <i>comparable</i>; that is, the first operand +must be <a href="#Assignment_compatibility">assignment compatible</a> +with the type of the second operand, or vice versa. <p> -Operands of boolean type are equal if they are either both <code>true</code> -or both <code>false</code>. </p> -<p> -The rules for comparison of composite types are described in the -section on §<a href="#Comparison_compatibility">Comparison compatibility</a>. +The operators <code>==</code> and <code>!=</code> apply +to operands of all types except arrays and structs. +All other comparison operators apply only to integer, floating-point +and string values. The result of a comparison is defined as follows: </p> +<ul> + <li> + Integer values are compared in the usual way. + </li> + <li> + Floating point values are compared as defined by the IEEE-754 + standard. + </li> + <li> + Two complex values <code>u</code>, <code>v</code> are + equal if both <code>real(u) == real(v)</code> and + <code>imag(u) == imag(v)</code>. + </li> + <li> + String values are compared byte-wise (lexically). + </li> + <li> + Boolean values are are equal if they are either both + <code>true</code> or both <code>false</code>. + </li> + <li> + Pointer values are equal if they point to the same location + or if both are <code>nil</code>. + </li> + <li> + Function values are equal if they refer to the same function + or if both are <code>nil</code>. + </li> + <li> + A slice value may only be compared to <code>nil</code>. + </li> + <li> + Channel and map values are equal if they were created by the same call to <code>make</code> + (§<a href="#Making_slices_maps_and_channels">Making slices, maps, and channels</a>) + or if both are <code>nil</code>. + </li> + <li> + Interface values are equal if they have identical dynamic types and + equal dynamic values or if both are <code>nil</code>. + </li> + <li> + An interface value <code>x</code> is equal to a non-interface value + <code>y</code> if the dynamic type of <code>x</code> is identical to + the static type of <code>y</code> and the dynamic value of <code>x</code> + is equal to <code>y</code>. + </li> + <li> + A pointer, function, slice, channel, map, or interface value is equal + to <code>nil</code> if it has been assigned the explicit value + <code>nil</code>, if it is uninitialized, or if it has been assigned + another value equal to <code>nil</code>. + </li> +</ul> + <h3 id="Logical_operators">Logical operators</h3> |