#
A fold expression performs a fold of a pack ([temp.variadic]) over a binary operator.
fold-expression:
( cast-expression fold-operator .. )
( .. fold-operator cast-expression )
( cast-expression fold-operator .. fold-operator cast-expression )
fold-operator: one of
+   -   *   /   %   ^   &   |   <<   >>
+=  -=  *=  /=  %=  ^=  &=  |=  <<=  >>=  =
==  !=  <   >   <=  >=  &&  ||  ,   .*   ->*
2
#
An expression of the form (. op e) where op is a fold-operator is called a unary left fold.
An expression of the form (e op ..) where op is a fold-operator is called a unary right fold.
Unary left folds and unary right folds are collectively called unary folds.
In a unary fold, the cast-expression shall contain an unexpanded pack ([temp.variadic]).
3
#
An expression of the form (e1 op1 .. op2 e2) where op1 and op2 are fold-operators is called a binary fold.
In a binary fold, op1 and op2 shall be the same fold-operator, and either e1 shall contain an unexpanded pack or e2 shall contain an unexpanded pack, but not both.
If e2 contains an unexpanded pack, the expression is called a binary left fold.
If e1 contains an unexpanded pack, the expression is called a binary right fold.
[Example 1: template<typename ..Args> bool f(Args ..args) { return (true && .. && args); / OK } template<typename ..Args> bool f(Args ..args) { return (args + .. + args); / error: both operands contain unexpanded packs } — end example]
4
#
A fold expression is a pack expansion.

Follow Lee on X/Twitter - Father, Husband, Serial builder creating AI, crypto, games & web tools. We are friends :) AI Will Come To Life!

Check out: eBank.nz (Art Generator) | Netwrck.com (AI Tools) | Text-Generator.io (AI API) | BitBank.nz (Crypto AI) | ReadingTime (Kids Reading) | RewordGame | BigMultiplayerChess | WebFiddle | How.nz | Helix AI Assistant