Null object: Difference between revisions
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<syntaxhighlight lang="java">
module NullObject {
void run() {
@Inject Console console;
console.print($"Null value={Null}, Null.toString()={Null.toString()}");
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String? s = Null; // "String?" is shorthand for the union "Nullable|String"
String s2 = "test";
console.print($"{s=
// Int len = s.size; // <-- compiler error: String? does not have a "size" property
Int len = s?.size : 0;
console.print($"{len=
if (String test ?= s) {
// "s" is still Null in this test, we never get here
} else
s = "a non-null value";
// if (String test ?= s){} // <-- compiler error: The expression type is not nullable
s2 = s; // at this point, s is known to be a non-null String
console.print($"{s=
}
}
</syntaxhighlight>
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<pre>
Null value=Null, Null.toString()=Null
s=Null, s2=test,
len=0
s=a non-null value, s2=a non-null value,
</pre>
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nil</syntaxhighlight>
=={{header|
<syntaxhighlight lang="emal">
^|
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int b # defaults to 0
void c # only one allowed value: null
writeLine("nullable var equals
writeLine("type of a equals to Void data type: " + (generic!a == void)) # true
writeLine("integer value " + b + " equals to null: " + (b == null)) # allowed, always false
writeLine("a void value equals to null: " + (c == null)) # always true</syntaxhighlight>
</syntaxhighlight>▼
{{out}}
<pre>
nullable var equals
type of a equals to Void data type: ⊤
integer value 0 equals to null: ⊥
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</pre>
=={{header|GDScript}}==
Godot has a null value. Here is an example of dealing with null.
<syntaxhighlight lang="gdscript">
extends Node2D
func _ready() -> void:
var empty : Object
var not_empty = Object.new()
# Compare with null.
if empty == null:
print("empty is null")
else:
print("empty is not null")
# C-like comparation.
if not_empty:
print("not_empty is not null")
else:
print("not_empty is null")
return
▲</syntaxhighlight>
{{out}}
<pre>
empty is null
not_empty is not null
</pre>
=={{header|Go}}==
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=={{header|langur}}==
Null can be compared for directly, using equality operators
<syntaxhighlight lang="langur">val .x, .y = true, null
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It is always easy to test for nullness either by querying a variable's type or checking the value of a boolean expression involving a potentially null variable.
<syntaxhighlight lang="
var s
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