blocks|key|1765462|text|嗯，不是100%25，如果PHP支持自动生动，但你发布的语法在大部分情况下是有效的。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1765463|//+Works+as+you+have+assigned+a+value+of+'hello'
$a['a'][4][6]['b']+=+"hello";
var_dump($a);
echo+print_r($a,true);

//+works+as+you+have+assigned+a+value+of+'world'
$b[][][][]+=+"world";
var_dump($b);
echo+print_r($b,true);

//+ERROR:+Cannot+use+[]+for+reading
$c[];
var_dump($c);
echo+print_r($c,true);|code-block|syntax|javascript|1765464|无法使用[]读取：Related+Link|offset|length|1765465|entityMap|0|LINK|mutability|MUTABLE|url|https://stackoverflow.com/questions/3820258/cannot-use-for-reading^0|0|0|9|C|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|T|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|U|8|@]|9|@$I|V|J|W|1|X]]|A|$]]|$1|K|3|-4|5|6|7|Y|8|@]|9|@]|A|$]]]|L|$M|$5|N|O|P|A|$Q|R]]]]

Well not 100% if PHP supports autovivification but the syntax you posts works for the most part.

<pre><code>// Works as you have assigned a value of 'hello'
$a['a'][4][6]['b'] = "hello";
var_dump($a);
echo print_r($a,true);

// works as you have assigned a value of 'world'
$b[][][][] = "world";
var_dump($b);
echo print_r($b,true);

// ERROR: Cannot use [] for reading
$c[];
var_dump($c);
echo print_r($c,true);
</code></pre>

Cannot use [] for reading: <a href="https://stackoverflow.com/questions/3820258/cannot-use-for-reading">Related Link</a>

blocks|key|1978954|text|在perl中，项在检查时会自动激活，不需要赋值。到达最里面的请求密钥所需的项的路径将在检查时创建。请注意，{d+=>+undef}+is条目并不是实际创建的，而是隐含的。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1978955|+++use+strict;
+++use+warnings;
+++use+Data::Dumper;

+++my+%25a;+++++++#+as+is+empty,+equivalent+to+\%25a+is+{};
+++print+Dumper+%25a;
+++$a{b}{c}{d};+#+\%25a+is+now+{+b+=>+{+c+=>+{}}}
++++++++++++++++#+returns+an+undef+value.
+++print+Dumper+\%25a;|code-block|syntax|javascript|1978956|输出：|1978957|$VAR1+=+{};
$VAR1+=+{
++++++++++'b'+=>+{
+++++++++++++++++++'c'+=>+{}
+++++++++++++++++}
++++++++};|1978958|perl数组示例：|1978959|use+strict;
use+warnings;
use+Data::Dumper;

my+(@b,@c);++++++++++#+@b=(),+@c=()
print+Dumper+\@b;
$b[3];+++++++++++++++#+@b=()+aka+unchanged.
print+Dumper+\@b;
$b[3][2][1];+++++++++#+@b=(undef,undef,undef,[undef,undef,[]])
print+Dumper+\@b;
print+Dumper+\@c;
$c[3]=1++;+++++++++++#+@c=(undef,undef,undef,1)
print+Dumper+\@c;|1978960|1978961|Useless+use+of+array+element+in+void+context+at+-e+line+7.
Useless+use+of+array+element+in+void+context+at+-e+line+9.
$VAR1+=+[];
$VAR1+=+[];
$VAR1+=+[
++++++++++undef,
++++++++++undef,
++++++++++undef,
++++++++++[
++++++++++++undef,
++++++++++++undef,
++++++++++++[]
++++++++++]
++++++++];
$VAR1+=+[];
$VAR1+=+[
++++++++++undef,
++++++++++undef,
++++++++++undef,
++++++++++1
++++++++];|1978962|entityMap^0|0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|T|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|U|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|V|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|W|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|X|8|@]|9|@]|A|$]]|$1|M|3|N|5|D|7|Y|8|@]|9|@]|A|$E|F]]|$1|O|3|H|5|6|7|Z|8|@]|9|@]|A|$]]|$1|P|3|Q|5|D|7|10|8|@]|9|@]|A|$E|F]]|$1|R|3|-4|5|6|7|11|8|@]|9|@]|A|$]]]|S|$]]

in perl, items will autovivify upon inspection, assignment is not necessary. The path of items necessary to get to the innermost requested key will be created upon inspection. Note that the {d => undef} is entry is not actually created but is implied.

<pre><code> use strict;
 use warnings;
 use Data::Dumper;

 my %a; # as is empty, equivalent to \%a is {};
 print Dumper %a;
 $a{b}{c}{d}; # \%a is now { b =&gt; { c =&gt; {}}}
 # returns an undef value.
 print Dumper \%a;
</code></pre>

output:

<pre><code>$VAR1 = {};
$VAR1 = {
 'b' =&gt; {
 'c' =&gt; {}
 }
 };
</code></pre>

perl array example:

<pre><code>use strict;
use warnings;
use Data::Dumper;

my (@b,@c); # @b=(), @c=()
print Dumper \@b;
$b[3]; # @b=() aka unchanged.
print Dumper \@b;
$b[3][2][1]; # @b=(undef,undef,undef,[undef,undef,[]])
print Dumper \@b;
print Dumper \@c;
$c[3]=1 ; # @c=(undef,undef,undef,1)
print Dumper \@c;
</code></pre>

Output:

<pre><code>Useless use of array element in void context at -e line 7.
Useless use of array element in void context at -e line 9.
$VAR1 = [];
$VAR1 = [];
$VAR1 = [
 undef,
 undef,
 undef,
 [
 undef,
 undef,
 []
 ]
 ];
$VAR1 = [];
$VAR1 = [
 undef,
 undef,
 undef,
 1
 ];
</code></pre>

Searching <a href="http://uk3.php.net/manual-lookup.php?pattern=autovivification" rel="noreferrer">PHP.net</a> for autovivification gives no results. At the time of writing, <a href="http://en.wikipedia.org/wiki/Autovivification" rel="noreferrer">Wikipedia</a> claims that only Perl has it. There are no clearly definitive results when searching <a href="http://www.google.com/search?q=php%20autovivification" rel="noreferrer">Google</a> for "php autovivification". 

This PHP code runs fine:

<pre><code>$test['a'][4][6]['b'] = "hello world";
var_dump($test);

array
 'a' =&gt; 
 array
 4 =&gt; 
 array
 'b' =&gt; 
 array
 ...
</code></pre>

Can anyone provide a canonical answer (preferably with references) that PHP does have this feature, and any details such as the version it was introduced in, quirks, shortcuts etc?

Does PHP have autovivification?

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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在上搜索自动生动没有得到任何结果。在撰写本文时，声称只有Perl拥有它。在中搜索"php autovivification“没有明确的结果。这段PHP代码运行良好：$test['a'][4][6]['b'] = "hello world";var_dump($test);array  'a' =>     array ...

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