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PHP Programming / Data Type

PHP Programming / Data Type

  • PHP: Introduction - Manual

    • PHP supports ten PRIMITIVE types.

      Four SCALAR types:

      • boolean
      • integer
      • float (floating-point number, aka double)
      • string

      Four COMPOUND types:

      • array
      • object
      • callable
      • iterable

      And finally two special types:

      • resource
      • NULL

    • This manual also introduces some PSEUDO-TYPES for readability reasons: #ril

      • mixed
      • number
      • callback (aka callable)
      • array|object
      • void

      And the pseudo-variable $....

      可以解釋成 "and so on"，表示可以接受任意多個參數。

    • Some references to the type "double" may remain in the manual. Consider double the same as float; the two names exist only for historic reasons.

    • The type of a variable is not usually set by the programmer; rather, it is decided at runtime by PHP depending on the CONTEXT in which that variable is used.

    • Note: To check the TYPE AND VALUE of an expression, use the var_dump() function.

      To get a human-readable representation of a type FOR DEBUGGING, use the gettype() function.

      覺得 var_dump() 跟 gettype() 都可以用在 debugging，只是前者會印出內容，後者不會。

      To CHECK for a certain type, do not use gettype(), but rather the is_type functions. (指 is_int()、is_string() 等) Some examples:

      <?php
$a_bool = TRUE;   // a boolean
$a_str  = "foo";  // a string
$a_str2 = 'foo';  // a string
$an_int = 12;     // an integer

echo gettype($a_bool); // prints out:  boolean
echo gettype($a_str);  // prints out:  string

// If this is an integer, increment it by four
if (is_int($an_int)) {
    $an_int += 4;
}

// If $a_bool is a string, print it out
// (does not print out anything)
if (is_string($a_bool)) {
    echo "String: $a_bool";
}
?>

    • To forcibly convert a variable to a certain type, either CAST the variable or use the settype() function on it.

    • 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 TYPE JUGGLING.

      The type comparison tables may also be useful, as they show examples of various type-related comparisons.

Type Juggling/Casting

Boolean

  • PHP: Booleans - Manual #ril

    • This is the simplest type. A boolean expresses a truth value. It can be either TRUE or FALSE.

    Syntax

    • To specify a boolean literal, use the constants TRUE or FALSE. Both are CASE-INSENSITIVE.

      <?php
$foo = True; // assign the value TRUE to $foo
?>

      PHP 有些地方是 case insensitive，這對於團隊合作是個缺點，只能靠工具來檢查，讓大家寫法一致 ??

    • Typically, the result of an operator which returns a boolean value is passed on to a control structure.

      <?php
// == is an operator which tests
// equality and returns a boolean
if ($action == "show_version") {
    echo "The version is 1.23";
}

// this is not necessary...
if ($show_separators == TRUE) {
    echo "<hr>\n";
}

// ...because this can be used with exactly the same meaning:
if ($show_separators) {
    echo "<hr>\n";
}
?>

    Converting to boolean

    • To explicitly convert a value to boolean, use the (bool) or (boolean) casts. However, in most cases the cast is unnecessary, since a value will be automatically converted if an operator, function or control structure requires a boolean argument.

    • When converting to boolean, the following values are considered FALSE:

      • the boolean FALSE itself

      • the integers 0 and -0 (zero)

      • the floats 0.0 and -0.0 (zero)

      • the empty string, and the STRING "0"

        "0" 也被認定為 false，感覺有點雷?

      • an array with zero elements

      • the special type NULL (including UNSET VARIABLES)

      • SimpleXML objects created from empty tags

      Every other value is considered TRUE (including any resource and NAN).

      <?php
var_dump((bool) "");        // bool(false)
var_dump((bool) 1);         // bool(true)
var_dump((bool) -2);        // bool(true)
var_dump((bool) "foo");     // bool(true)
var_dump((bool) 2.3e5);     // bool(true)
var_dump((bool) array(12)); // bool(true)
var_dump((bool) array());   // bool(false)
var_dump((bool) "false");   // bool(true)
?>

    • Warning: -1 is considered TRUE, like any other non-zero (whether negative or positive) number!

參考資料 {: #reference }

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