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Started to clean up the structure, adding some content

Browse source 
in place of TODO comments, and more examples. Also cleaned
up a bit in the formatting.


git-svn-id: https://svn.php.net/repository/phpdoc/en/trunk@102552 c90b9560-bf6c-de11-be94-00142212c4b1
This commit is contained in:
Gabor Hojtsy 2002-11-04 15:45:11 +00:00
parent 51e24ab11f
commit 69e4f3f0be
1 changed files with 119 additions and 93 deletions
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212
language/types.xml
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@ -1,5 +1,5 @@
<?xml version="1.0" encoding="iso-8859-1"?>
<!-- $Revision: 1.93 $ -->
<!-- $Revision: 1.94 $ -->
<chapter id="language.types">
<title>Types</title>
@ -7,12 +7,11 @@
<title>Introduction</title>
<simpara>
PHP supports eight primitive <!-- (all types are primitive in php) -->
types.
PHP supports eight primitive types.
</simpara>
<para>
Four scalar <!-- (basic, can't be split into parts) --> types:
Four scalar types:
<itemizedlist>
@ -103,10 +102,11 @@
</listitem>
</itemizedlist>
You may also find some references to the type "double". Consider
double the same as float, the two names exist only for historic
reasons.
</para>
<simpara>
The type of a variable is usually not set by the programmer;
rather, it is decided at runtime by PHP depending on the context in
@ -118,13 +118,36 @@
linkend="language.expressions">expression</link>, use
<function>var_dump</function>.
</simpara>
<simpara>
<para>
If you simply want a human-readable representation of the type for
debugging, use <function>gettype</function>. To check for a certain type,
do <emphasis>not</emphasis> use <function>gettype</function>, but use the
<literal>is_<replaceable>type</replaceable></literal> functions.
</simpara>
<!-- TODO: example(s) would be great -->
<literal>is_<replaceable>type</replaceable></literal> functions. Some
examples:
<informalexample>
<programlisting role="php">
<![CDATA[
$bool = TRUE; // a boolean
$str = "foo"; // a string
$int = 12; // an integer
echo gettype($bool); // prints out "boolean"
echo gettype($str); // prints out "string"
// If this is an integer, increment it by four
if (is_int($int)) {
$int += 4;
}
// If $bool is a string, print it out
// (does not print out anything)
if (is_string($bool)) {
echo "String: $bool";
}
]]>
</programlisting>
</informalexample>
</para>
</note>
<simpara>
If you would like to force a variable to be converted to a certain
@ -133,22 +156,19 @@
use the <function>settype</function> function on it.
</simpara>
<simpara>
Note that a variable may behave in different manners in certain
Note that a variable may be evaluated with different values in certain
situations, depending on what type it is at the time. For more
information, see the section on <link
linkend="language.types.type-juggling">Type Juggling</link>.
</simpara>
</sect1>
</sect1>
<sect1 id="language.types.boolean">
<title>Booleans</title>
<simpara>
This is the easiest type. A <type>boolean</type> expresses a
truth value. It can be either &true; or
&false;.
truth value. It can be either &true; or &false;.
</simpara>
<note>
@ -162,11 +182,10 @@
<para>
To specify a boolean literal, use either the keyword &true;
or &false;. Both are case-insensitive.
<!-- technically they are just constants -->
<informalexample>
<programlisting role="php">
<![CDATA[
$foo = True; // assign the value TRUE to $foo
$foo = True; // assign the value TRUE to $foo
]]>
</programlisting>
</informalexample>
@ -180,17 +199,18 @@ $foo = True; // assign the value TRUE to $foo
<informalexample>
<programlisting role="php">
<![CDATA[
// == is an operator which returns a boolean
// == is an operator which test
// equality and returns a boolean
if ($action == "show_version") {
echo "The version is 1.23";
}
// this is not necessary:
// this is not necessary...
if ($show_separators == TRUE) {
echo "<hr>\n";
}
// because you can simply type this:
// ...because you can simply type
if ($show_separators) {
echo "<hr>\n";
}
@ -220,7 +240,7 @@ if ($show_separators) {
<itemizedlist>
<listitem>
<simpara>the <link linkend="language.types.boolean">boolean</link>
&false;<!-- duh... --></simpara>
&false; itself</simpara>
</listitem>
<listitem>
<simpara>the <link linkend="language.types.integer">integer</link
@ -260,12 +280,21 @@ if ($show_separators) {
or positive) number!
</simpara>
</warning>
<!-- TODO: add a few examples, for the people only looking at
the examples... -->
<informalexample>
<programlisting role="php">
<![CDATA[
echo gettype((bool) ""); // bool(false)
echo gettype((bool) 1); // bool(true)
echo gettype((bool) -2); // bool(true)
echo gettype((bool) "foo"); // bool(true)
echo gettype((bool) 2.3e5); // bool(true)
echo gettype((bool) array(12)); // bool(true)
echo gettype((bool) array()); // bool(false)
]]>
</programlisting>
</informalexample>
</para>
</sect2>
</sect2>
</sect1>
<sect1 id="language.types.integer">
@ -303,20 +332,23 @@ $a = 0x1A; # hexadecimal number (equivalent to 26 decimal)
]]>
</programlisting>
</example>
<!--
Formally the possible structure for integer literals is:
<informalexample>
<programlisting>
<![CDATA[
decimal : [1-9][0-9]*
| 0
decimal : [1-9][0-9]*
| 0
hexadecimal : 0[xX][0-9a-fA-F]+
octal : 0[0-7]+
integer : [+-]?decimal
| [+-]?hexadecimal
| [+-]?octal
-->
hexadecimal : 0[xX][0-9a-fA-F]+
octal : 0[0-7]+
integer : [+-]?decimal
| [+-]?hexadecimal
| [+-]?octal
]]>
</programlisting>
</informalexample>
The size of an integer is platform-dependent, although a
maximum value of about two billion is the usual value
(that's 32 bits signed). PHP does not support unsigned
@ -372,13 +404,15 @@ var_dump($large_number);
<para>
There is no integer division operator in PHP.
<literal>1/2</literal> yields the <type>float</type>
<literal>0.5</literal>. <!-- See ??? for more information. (with the
operators, or with type-jug) -->
<literal>0.5</literal>. You can cast the value to
an integer to always round it downwards, or you can
use the <function>round</function> function.
<informalexample>
<programlisting role="php">
<![CDATA[
var_dump( 25/7 );
// output: float(3.5714285714286)
var_dump(25/7); // float(3.5714285714286)
var_dump((int) (25/7)); // int(3)
var_dump(round(25/7)); // float(4)
]]>
</programlisting>
</informalexample>
@ -420,7 +454,6 @@ var_dump( 25/7 );
<para>
If the float is beyond the boundaries of integer
<!-- usually, or is it 'always'? -->
(usually <literal>+/- 2.15e+9 = 2^31</literal>),
the result is undefined, since the float hasn't
got enough precision to give an exact integer result.
@ -449,7 +482,7 @@ echo (int) ( (0.1+0.7) * 10 ); // echoes 7!
<title>From strings</title>
<simpara>
See <link linkend="language.types.string.conversion">String
conversion</link>
conversion to numbers</link>
</simpara>
</sect3>
@ -467,16 +500,7 @@ echo (int) ( (0.1+0.7) * 10 ); // echoes 7!
</simpara>
</caution>
</para>
<!--
IMO, it would more sense as (int) $arr returned the
number of elements in $arr. This won't break anything,
since this behaviour was never defined before, and
(bool)(int) $arr will still behave the same.
-->
</sect3>
</sect2>
</sect1>
@ -485,20 +509,24 @@ echo (int) ( (0.1+0.7) * 10 ); // echoes 7!
<para>
Floating point numbers (AKA "floats", "doubles" or "real numbers") can be
specified using any of the following syntaxes:
<synopsis>
<informalexample>
<programlisting role="php">
$a = 1.234; $a = 1.2e3; $a = 7E-10;
</synopsis>
<!--
LNUM [0-9]+
DNUM ([0-9]*[\.][0-9]+)|([0-9]+[\.][0-9]*)
EXPONENT_DNUM (({LNUM}|{DNUM})[eE][+-]?{LNUM})
-->
</programlisting>
</informalexample>
Formally:
<informalexample>
<programlisting role="php">
LNUM [0-9]+
DNUM ([0-9]*[\.]{LNUM}) | ({LNUM}[\.][0-9]*)
EXPONENT_DNUM ( ({LNUM} | {DNUM}) [eE][+-]? {LNUM})
</programlisting>
</informalexample>
The size of a float is platform-dependent,
although a maximum of ~1.8e308 with a precision of roughly 14
decimal digits is a common value (that's 64 bit IEEE format).
</para>
<warning id="warn.float-precision">
<title>Floating point precision</title>
<para>
@ -526,14 +554,16 @@ EXPONENT_DNUM (({LNUM}|{DNUM})[eE][+-]?{LNUM})
</para>
</warning>
<!-- TODO: add more info -->
<sect2 id="language.types.float.casting">
<title>Converting to float</title>
<para>
For information on when and how strings are converted to floats,
see the section titled <link linkend="language.types.string.conversion">String
conversion to numbers</link>.
conversion to numbers</link>. For values of other types, the conversion
is the same as if the value would have been converted to integer
and then to float. See the <link linkend="language.types.integer.casting">Converting
to integer</link> section for more information.
</para>
</sect2>
</sect1>
@ -544,10 +574,8 @@ EXPONENT_DNUM (({LNUM}|{DNUM})[eE][+-]?{LNUM})
A <type>string</type> is series of characters. In PHP,
a character is the same as a byte, that is, there are exactly
256 different characters possible. This also implies that PHP
has no native support of Unicode.
<!-- how about unicode? will we support that eventually? Are
there current any ways to work with unicode?
-->
has no native support of Unicode. See <function>utf8_enncode</function>
and <function>utf8_decode</function> for some Unicode support.
</para>
<note>
<simpara>
@ -589,19 +617,19 @@ EXPONENT_DNUM (({LNUM}|{DNUM})[eE][+-]?{LNUM})
enclose it in single quotes (the character <literal>'</literal>).
</para>
<para>
To specify a literal single
To specify a literal single
quote, you will need to escape it with a backslash
(<literal>\</literal>), like in many other languages.
If a backslash needs to occur before a single quote or at
the end of the string, you need to double it.
Note that if you try to escape any
other character, the backslash too will be printed! So
other character, the backslash will also be printed! So
usually there is no need to escape the backslash itself.
<note>
<simpara>
In PHP 3, a warning will
be issued at the <literal>E_NOTICE</literal> level when this
happens.
happens.
</simpara>
</note>
<note>
@ -614,8 +642,8 @@ EXPONENT_DNUM (({LNUM}|{DNUM})[eE][+-]?{LNUM})
<programlisting role="php">
<![CDATA[
echo 'this is a simple string';
echo 'You can also have embedded newlines in strings,
like this way.';
echo 'You can also have embedded newlines in strings
this way';
echo 'Arnold once said: "I\'ll be back"';
// output: ... "I'll be back"
echo 'Are you sure you want to delete C:\\*.*?';
@ -692,7 +720,7 @@ echo 'I am trying to include at this point: \n a newline';
backslash will be printed too!
</para>
<para>
But the most important pre of double-quoted strings
But the most important feature of double-quoted strings
is the fact that variable names will be expanded.
See <link linkend="language.types.string.parsing">string
parsing</link> for details.
@ -706,10 +734,10 @@ echo 'I am trying to include at this point: \n a newline';
("&lt;&lt;&lt;"). One should provide an identifier after
<literal>&lt;&lt;&lt;</literal>, then the string, and then the
same identifier to close the quotation.
</simpara>
</simpara>
<simpara>
The closing identifier <emphasis>must</emphasis> begin in the
first column of the line. Also, the identifier used must follow
first column of the line. Also, the identifier used must follow
the same naming rules as any other label in PHP: it must contain
only alphanumeric characters and underscores, and must start with
a non-digit character or underscore.
@ -776,14 +804,13 @@ EOT;
Heredoc support was added in PHP 4.
</para>
</note>
</sect3>
<sect3 id="language.types.string.parsing">
<title>Variable parsing</title>
<simpara>
When a string is specified in double quotes or with
heredoc, variables are
parsed within it.
heredoc, variables are parsed within it.
</simpara>
<simpara>
There are two types of syntax, a
@ -795,11 +822,10 @@ EOT;
to parse a variable, an array value, or an object property.
</simpara>
<simpara>
The complex syntax was introduced in PHP 4,
<!-- XXX was it? and starting with what version exactly? -->
and can be recognised
The complex syntax was introduced in PHP 4, and can be recognised
by the curly braces surrounding the expression.
</simpara>
<sect4 id="language.types.string.parsing.simple">
<title>Simple syntax</title>
<simpara>
@ -813,7 +839,7 @@ EOT;
<![CDATA[
$beer = 'Heineken';
echo "$beer's taste is great"; // works, "'" is an invalid character for varnames
echo "He drank some $beers"; // won't work, 's' is a valid character for varnames
echo "He drank some $beers"; // won't work, 's' is a valid character for varnames
echo "He drank some ${beer}s"; // works
]]>
</programlisting>
@ -827,19 +853,17 @@ echo "He drank some ${beer}s"; // works
the one with variables.
<!-- XXX isn't &true; :(, this would be the trick
Also,
the same trick with curly-braces works if you
want to limit the greediness of parsers (aren't they
paying them enough or something?).
Also, the same trick with curly-braces works if you
want to limit the greediness of parsers.
-->
</simpara>
<informalexample>
<programlisting role="php">
<![CDATA[
$fruits = array( 'strawberry' => 'red' , 'banana' => 'yellow' );
$fruits = array('strawberry' => 'red', 'banana' => 'yellow');
// note that this works differently outside string-quotes.
// note that this works differently outside string-quotes
echo "A banana is $fruits[banana].";
echo "This square is $square->width meters broad.";
@ -860,6 +884,7 @@ echo "This square is $square->{width}00 centimeters broad.";
For anything more complex, you should use the complex syntax.
</simpara>
</sect4>
<sect4 id="language.types.string.parsing.complex">
<title>Complex (curly) syntax</title>
<simpara>
@ -912,8 +937,9 @@ echo "I'd like to have another {${ strrev('reeb') }}, hips";
</para>
<note>
<simpara>
For backwards compatibility, you can still use the array-braces.
However, this syntax is deprecated as of PHP 4.
For backwards compatibility, you can still use array-braces
for the same purpose. However, this syntax is deprecated as
of PHP 4.
</simpara>
</note>
<para>