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an attempt to define initialization order within a package.

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DELTA=23  (19 added, 1 deleted, 3 changed)
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CL=34649
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Rob Pike 2009-09-15 11:56:39 -07:00
parent 678625d8df
commit 8cb9184d7f
1 changed files with 22 additions and 4 deletions
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26
doc/go_spec.html
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@ -764,7 +764,7 @@ a type named <code>T</code>:
A field declaration may be followed by an optional string literal <i>tag</i>, A field declaration may be followed by an optional string literal <i>tag</i>,
which becomes an attribute for all the identifiers in the corresponding which becomes an attribute for all the identifiers in the corresponding
field declaration. The tags are made field declaration. The tags are made
visible through a reflection library <font color=red>TODO: reference?</font> visible through a <a href="#Package_unsafe">reflection interface</a>
but are otherwise ignored. but are otherwise ignored.
</p> </p>
@ -2384,7 +2384,7 @@ its dynamic type is a structure whose sequential fields are the
trailing arguments of the call. That is, the actual arguments trailing arguments of the call. That is, the actual arguments
provided for a <code>...</code> parameter are wrapped into a struct provided for a <code>...</code> parameter are wrapped into a struct
that is passed to the function instead of the actual arguments. that is passed to the function instead of the actual arguments.
Using the reflection library (TODO: reference), <code>f</code> may Using the <a href="#Package_unsafe">reflection</a> interface, <code>f</code> may
unpack the elements of the dynamic type to recover the actual unpack the elements of the dynamic type to recover the actual
arguments. arguments.
</p> </p>
@ -4281,8 +4281,7 @@ var t T
<h3 id="Program_execution">Program execution</h3> <h3 id="Program_execution">Program execution</h3>
<p> <p>
A package with no imports is initialized by assigning initial values to A package with no imports is initialized by assigning initial values to
all its package-level variables in data-dependency order all its package-level variables
(<font color=red>TODO: clarify</font>)
and then calling any and then calling any
package-level function with the name and signature of package-level function with the name and signature of
</p> </p>
@ -4296,6 +4295,25 @@ than one source file, there may be more than one
only one per source file. only one per source file.
</p> </p>
<p> <p>
Within a package, package-level variables are initialized,
and constant values are determined, in
data-dependent order: if the initializer of <code>A</code>
depends on the value of <code>B</code>, <code>A</code>
will be set after <code>B</code>.
It is an error if such dependencies form a cycle.
Dependency analysis is done lexically: <code>A</code>
depends on <code>B</code> if the value of <code>A</code>
contains a mention of <code>B</code>, contains a value
whose initializer
mentions <code>B</code>, or mentions a function that
mentions <code>B</code>, recursively.
If two items are not interdependent, they will be initialized
in the order they appear in the source.
Since the dependency analysis is done per package, it can be
defeated if <code>A</code>'s initializer calls a function defined
in another package that refers to <code>B</code>.
</p>
<p>
Initialization code may contain "go" statements, but the functions Initialization code may contain "go" statements, but the functions
they invoke do not begin execution until initialization of the entire they invoke do not begin execution until initialization of the entire
program is complete. Therefore, all initialization code is run in a single program is complete. Therefore, all initialization code is run in a single