Null object: Difference between revisions
Content added Content deleted
(Add Ecstasy example) |
(Replace println() with print(); replace output "syntaxhighlight" tag with "pre" tag) |
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{ |
{ |
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@Inject Console console; |
@Inject Console console; |
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console. |
console.print($"Null value={Null}, Null.toString()={Null.toString()}"); |
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// String s = Null; // <-- compiler error: cannot assign Null to a String type |
// String s = Null; // <-- compiler error: cannot assign Null to a String type |
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String? s = Null; // "String?" is shorthand for the union "Nullable|String" |
String? s = Null; // "String?" is shorthand for the union "Nullable|String" |
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String s2 = "test"; |
String s2 = "test"; |
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console. |
console.print($"s={s}, s2={s2}, (s==s2)={s==s2}"); |
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// Int len = s.size; // <-- compiler error: String? does not have a "size" property |
// Int len = s.size; // <-- compiler error: String? does not have a "size" property |
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Int len = s?.size : 0; |
Int len = s?.size : 0; |
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console. |
console.print($"len={len}"); |
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if (String test ?= s) |
if (String test ?= s) |
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} |
} |
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// |
// if (String test ?= s){} // <-- compiler error: The expression type is not nullable: "String" |
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s2 = s; // at this point, s is known to be a non-null String |
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if (String test ?= s) |
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console.print($"s={s}, s2={s2}, (s==s2)={s==s2}"); |
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{ |
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// the variable "test" is definitely assigned here |
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console.println($"test={test}"); |
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} |
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else |
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{ |
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// s2 = test; // <-- compiler error: "test" is not definitely assigned |
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} |
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} |
} |
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} |
} |
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</syntaxhighlight> |
</syntaxhighlight> |
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{{out}} |
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Output: |
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<pre> |
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<syntaxhighlight> |
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Null value=Null, Null.toString()=Null |
Null value=Null, Null.toString()=Null |
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s=Null, s2=test, (s==s2)=False |
s=Null, s2=test, (s==s2)=False |
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len=0 |
len=0 |
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s=a non-null value, s2=a non-null value, (s==s2)=True |
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</pre> |
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</syntaxhighlight> |
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=={{header|Eiffel}}== |
=={{header|Eiffel}}== |
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