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Optional chaining operators allow accessing nested object properties
in a secure manner, without the need to check the entire reference
chain for validity.
1. The `?.` operator can be used to lookup a named property in a
left-hand side expression without having to check whether the lhs
value is a proper object.
-- Expect stdout --
true
true
-- End --
-- Testcase --
{%
obj = { foo: 1 };
print(obj.bar?.baz == null, "\n"); // obj.bar is null
print(obj.foo?.bar == null, "\n"); // obj.foo is not an object
%}
-- End --
2. The `?.[…]` operator complements the `?.` one and applies the
same semantics to computed property accesses.
-- Expect stdout --
true
true
true
true
-- End --
-- Testcase --
{%
obj = { foo: 1 };
arr = [ 1, 2 ];
print(obj["bar"]?.["baz"] == null, "\n"); // obj.bar is null
print(obj["foo"]?.["bar"] == null, "\n"); // obj.foo is not an object
print(arr[0]?.["foo"] == null, "\n"); // arr[0] is not an object
print(foo?.[1] == null, "\n"); // foo is not an array
%}
-- End --
3. The `?.(…)` function call operator yields `null` when the left-hand
side value is not a callable function value.
-- Expect stdout --
true
true
-- End --
-- Testcase --
{%
foo = 1;
print(foo?.(1, 2, 3) == null, "\n"); // foo is not a function
print(bar?.("test") == null, "\n"); // bar is null
%}
-- End --
4. Optional chaining operators cannot be used on the left-hand side of
an assignment or increment/decrement expression.
-- Expect stderr --
Syntax error: Invalid left-hand side expression for assignment
In line 2, byte 13:
` obj?.foo = 1;`
Near here -----^
-- End --
-- Testcase --
{%
obj?.foo = 1;
%}
-- End --
-- Expect stderr --
Syntax error: Invalid increment/decrement operand
In line 2, byte 7:
` obj?.foo++;`
^-- Near here
-- End --
-- Testcase --
{%
obj?.foo++;
%}
-- End --
|
