c++11 - C++ function returning function -

where in standard functions returning functions disallowed? understand conceptually ridiculous, seems me grammar allow them. according webpage, "noptr-declarator [is] valid declarator" include declarator of function:

int f()(); 

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regarding syntax.

it seems me syntax, spelled out in [dcl.decl], allows

int f(char)(double) 

which interpreted the function f that takes a char and returns function same signature as int g(double).

1    declarator: 2       ptr-declarator 3       noptr-declarator parameters-and-qualifiers trailing-return-type 4    ptr-declarator: 5        noptr-declarator 6        ptr-operator ptr-declarator 7    noptr-declarator: 8        declarator-id attribute-specifier-seq opt 9        noptr-declarator parameters-and-qualifiers 10       noptr-declarator [ constant-expression opt ] attribute-specifier-seq opt 11       ( ptr-declarator ) 12    parameters-and-qualifiers: 13       ( parameter-declaration-clause ) cv-qualifier-seqafter 

roughly speaking, after 1->2, 2=4, 4->6, 4->6 should have ptr-operator ptr-operator ptr-operator then, use 4->5, 5=7, 7->8 first declarator; use 4->5, 5=7, 7->9 second , third declarators.

from [dcl.fct], pretty explicitly:

functions shall not have return type of type array or function, although may have return type of type pointer or reference such things. there shall no arrays of functions, although there can arrays of pointers functions.

with c++11, want:

std::function<int()> f(); std::function<int(double)> f(char); 

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there confusion regarding c++ grammar. statement int f(char)(double); can parsed according grammar. here parse tree:

furthermore such parse meaningful based on [dcl.fct]/1:

in declaration t d d has form
    d1 ( parameter-declaration-clause ) cv-qualifier-seq_opt
        ref-qualifier_opt exception-specification_opt attribute-specifier-seq_opt
, type of contained declarator-id in declaration t d1 “derived-declarator-type-list t”, type of declarator-id in d “derived-declarator-type-list function of (parameter-declaration-clause ) cv-qualifier-seq_opt ref-qualifier_opt returning t”.

in example t == int, d == f(char)(double), d1 == f(char). type of declarator-id in t d1 (int f(char)) "function of (char) returning int". derived-declarator-type-list "function of (char) returning". thus, type of f read "function of (char) returning function of (double) returning int."

it's ado nothing, explicitly disallowed declarator form. not grammar.