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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)
OCL=34646
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>,
which becomes an attribute for all the identifiers in the corresponding
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.
</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
provided for a <code>...</code> parameter are wrapped into a struct
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
arguments.
</p>
@ -4281,8 +4281,7 @@ var t T
<h3 id="Program_execution">Program execution</h3>
<p>
A package with no imports is initialized by assigning initial values to
all its package-level variables in data-dependency order
(<font color=red>TODO: clarify</font>)
all its package-level variables
and then calling any
package-level function with the name and signature of
</p>
@ -4296,6 +4295,25 @@ than one source file, there may be more than one
only one per source file.
</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
they invoke do not begin execution until initialization of the entire
program is complete. Therefore, all initialization code is run in a single