I have this sample of code:
struct S {};
S s = S();
Per my understanding, I see that s = S() in the declaration S s = S() is an init-declarator where s is a declarator and = S() is an initializer.
Also, I see that the initializer (= S()) is a brace-or-equal-initializer which is "= initializer-clause". This means finally that S() is an initializer-clause.
By the grammar, an initializer-clause is either an assignment-expression or a braced-init-list. Indeed, S() might not be a braced-init-list, but it may be an assignment-expression.
If my analysis is correct so far, I have a question here:
How S() is an assignment-expression? Where is the assignment-operator in expression S()?
In other words, the grammar of assignment-expression is:
assignment-expression:
conditional-expression
yield-expression
throw-expression
logical-or-expression assignment-operator initializer-clause
how S() could be one of the above?
Similarly, the grammar of a throw-expression is
throw-expression:
throw assignment-expression
how S() in statement throw S(); is an assignment-expression?
How
S()is an assignment-expression?
Because it matches the first option conditional-expression as shown below. Note the emphasized part in each section/part and that at the end we reach to simple-type-specifier ( expression-listopt ) which is S().
assignment-expression:
- conditional-expression
- yield-expression
- throw-expression
- logical-or-expression assignment-operator initializer-clause
Next, we go to conditional expression:
conditional-expression:
- logical-or-expression
- logical-or-expression ? expression : assignment-expression
Next, to logical-or-expression:
logical-or-expression:
- logical-and-expression
- logical-or-expression || logical-and-expression
Next, to logical-and-expression:
logical-and-expression:
- inclusive-or-expression
- logical-and-expression && inclusive-or-expression
From inclusive-or-expression:
inclusive-or-expression:
- exclusive-or-expression
- inclusive-or-expression | exclusive-or-expression
Next, exclusive-or-expression
exclusive-or-expression:
- and-expression
- exclusive-or-expression ^ and-expression
Now to and-expression
and-expression:
- equality-expression
- and-expression & equality-expression
From relational-operator
equality-expression:
- relational-expression
- equality-expression == relational-expression
- equality-expression != relational-expression
Next from relational-expression
relational-expression:
- compare-expression
- relational-expression < compare-expression
- relational-expression > compare-expression
- relational-expression <= compare-expression
- relational-expression >= compare-expression
Next to compare-expression
compare-expression:
- shift-expression
- compare-expression <=> shift-expression
Next to shift-expression
shift-expression:
- additive-expression
- shift-expression << additive-expression
- shift-expression >> additive-expression
Next additive-expression
additive-expression:
- multiplicative-expression
- additive-expression + multiplicative-expression
- additive-expression - multiplicative-expression
Next to multiplicative-expression
multiplicative-expression:
- pm-expression
- multiplicative-expression * pm-expression
- multiplicative-expression / pm-expression
- multiplicative-expression % pm-expression
Next to pm-expression
pm-expression:
- cast-expression
- pm-expression .* cast-expression
- pm-expression ->* cast-expression
Next to cast-expression
cast-expression:
- unary-expression
- ( type-id ) cast-expression
Next to unary-expression
unary-expression:
- postfix-expression
- unary-operator cast-expression
- ++ cast-expression
- -- cast-expression
- await-expression
- sizeof unary-expression
- sizeof ( type-id )
- sizeof ... ( identifier )
- alignof ( type-id )
- noexcept-expression
- new-expression
- delete-expression
Finally we reach postfix-expression
postfix-expression:
- primary-expression
- postfix-expression [ expression-listopt ]
- postfix-expression ( expression-listopt )
- simple-type-specifier ( expression-listopt )
- typename-specifier ( expression-listopt )
- simple-type-specifier braced-init-list
- typename-specifier braced-init-list
- postfix-expression . templateopt id-expression
- postfix-expression -> templateopt id-expression
- postfix-expression ++
- postfix-expression --
- dynamic_cast < type-id > ( expression )
- static_cast < type-id > ( expression )
- reinterpret_cast < type-id > ( expression )
- const_cast < type-id > ( expression )
- typeid ( expression )
- typeid ( type-id )