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cppdraft/exec/queryable/concept.md

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+[exec.queryable.concept]
+
+# 33 Execution control library [[exec]](./#exec)
+
+## 33.2 Queries and queryables [[exec.queryable]](exec.queryable#concept)
+
+### 33.2.2 queryable concept [exec.queryable.concept]
+
+namespace std {template<class T>concept [*queryable*](#concept:queryable "33.2.2 queryable concept [exec.queryable.concept]") = [destructible](concept.destructible#concept:destructible "18.4.10 Concept destructible [concept.destructible]")<T>; // *exposition only*}
+
+[1](#1)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/exec.tex#L159)
+
+The exposition-only [*queryable*](#concept:queryable "33.2.2 queryable concept [exec.queryable.concept]") concept specifies
+the constraints on the types of queryable objects[.](#1.sentence-1)
+
+[2](#2)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/exec.tex#L163)
+
+Let env be an object of type Env[.](#2.sentence-1)
+
+The type Env models [*queryable*](#concept:queryable "33.2.2 queryable concept [exec.queryable.concept]") if for each callable object q and a pack of subexpressions args,
+if requires { q(env, args...) } is true thenq(env, args...) meets any semantic requirements imposed by q[.](#2.sentence-2)

cppdraft/exec/queryable/general.md

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+[exec.queryable.general]
+
+# 33 Execution control library [[exec]](./#exec)
+
+## 33.2 Queries and queryables [[exec.queryable]](exec.queryable#general)
+
+### 33.2.1 General [exec.queryable.general]
+
+[1](#1)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/exec.tex#L115)
+
+A [*queryable object*](#def:object,queryable "33.2.1 General [exec.queryable.general]") is
+a read-only collection of key/value pair
+where each key is a customization point object known as a [*query object*](#def:query_object "33.2.1 General [exec.queryable.general]")[.](#1.sentence-1)
+
+A [*query*](#def:query "33.2.1 General [exec.queryable.general]") is an invocation of a query object
+with a queryable object as its first argument and
+a (possibly empty) set of additional arguments[.](#1.sentence-2)
+
+A query imposes syntactic and semantic requirements on its invocations[.](#1.sentence-3)
+
+[2](#2)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/exec.tex#L124)
+
+Let q be a query object,
+let args be a (possibly empty) pack of subexpressions,
+let env be a subexpression
+that refers to a queryable object o of type O, and
+let cenv be a subexpression referring to o such that decltype((cenv)) is const O&[.](#2.sentence-1)
+
+The expression q(env, args...) is equal to ([[concepts.equality]](concepts.equality "18.2 Equality preservation"))
+the expression q(cenv, args...)[.](#2.sentence-2)
+
+[3](#3)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/exec.tex#L134)
+
+The type of a query expression cannot be void[.](#3.sentence-1)
+
+[4](#4)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/exec.tex#L137)
+
+The expression q(env, args...) is
+equality-preserving ([[concepts.equality]](concepts.equality "18.2 Equality preservation")) and
+does not modify the query object or the arguments[.](#4.sentence-1)
+
+[5](#5)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/exec.tex#L142)
+
+If the expression env.query(q, args...) is well-formed,
+then it is expression-equivalent to q(env, args...)[.](#5.sentence-1)
+
+[6](#6)
+
+[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/exec.tex#L146)
+
+Unless otherwise specified,
+the result of a query is valid as long as the queryable object is valid[.](#6.sentence-1)