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build members of keyof mapped types lazily #64526

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85518a5
Resolve members of instantiated class and interface references lazily
maschwenk Sep 26, 2026
f035906
Answer shape queries on instantiated references without resolving mem…
maschwenk Sep 27, 2026
2efc063
Don't record members that are about to be resolved in full
maschwenk Sep 27, 2026
af2719b
Check for resolved members before taking the lazy paths
maschwenk Sep 27, 2026
cdac4e3
Read lazy member tables through the regular accessors
maschwenk Sep 27, 2026
0a06ad9
Merge main into perf/declared-shape-queries
maschwenk Sep 29, 2026
39ce30c
Drop the partial member handling now that #64372 is in
maschwenk Sep 29, 2026
d40b4bd
Simplify the lazy member lookup
maschwenk Sep 29, 2026
a5a5da9
Consolidate the tests into one
maschwenk Sep 29, 2026
2aefafb
Trim comments
maschwenk Sep 29, 2026
4df7b7d
Resolve members of keyof mapped types lazily
maschwenk Sep 29, 2026
05ead00
Add a test for lazily resolved mapped type members
maschwenk Sep 29, 2026
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509 changes: 433 additions & 76 deletions tsc/internal/checker/checker.go
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4 changes: 2 additions & 2 deletions tsc/internal/checker/relater.go
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Original file line number Diff line number Diff line change
Expand Up @@ -678,8 +678,8 @@ func (c *Checker) elaborateArrowFunction(node *ast.Node, source *Type, target *T
// and no required properties, call/construct signatures or index signatures
func (c *Checker) isWeakType(t *Type) bool {
if t.flags&TypeFlagsObject != 0 {
resolved := c.resolveStructuredTypeMembers(t)
return len(resolved.signatures) == 0 && len(resolved.indexInfos) == 0 && len(resolved.properties) > 0 && core.Every(resolved.properties, func(p *ast.Symbol) bool {
return len(c.getSignaturesOfStructuredType(t, SignatureKindCall)) == 0 && len(c.getSignaturesOfStructuredType(t, SignatureKindConstruct)) == 0 &&
len(c.getIndexInfosOfStructuredType(t)) == 0 && c.hasPropertiesOfStructuredType(t) && c.everyPropertyOfStructuredType(t, func(p *ast.Symbol) bool {
return p.Flags&ast.SymbolFlagsOptional != 0
})
}
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112 changes: 112 additions & 0 deletions tsc/testdata/baselines/reference/compiler/instantiatedReferenceLazyMembers.errors.txt
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Original file line number Diff line number Diff line change
@@ -0,0 +1,112 @@
instantiatedReferenceLazyMembers.ts(14,9): error TS2339: Property 'missing' does not exist on type 'Derived<number>'.
instantiatedReferenceLazyMembers.ts(22,5): error TS2341: Property 'secret' is private and only accessible within class 'Box<T>'.
instantiatedReferenceLazyMembers.ts(31,7): error TS2559: Type '{ other: number; }' has no properties in common with type 'Weak<"b">'.
instantiatedReferenceLazyMembers.ts(32,7): error TS2741: Property 'kind' is missing in type '{ other: number; }' but required in type 'Weak<"a">'.
instantiatedReferenceLazyMembers.ts(37,9): error TS2339: Property 'bind' does not exist on type 'Fn<"b">'.
instantiatedReferenceLazyMembers.ts(45,7): error TS2322: Type 'Dict<"b">' is not assignable to type '{ [key: string]: number; }'.
'string' index signatures are incompatible.
Type 'unknown' is not assignable to type 'number'.
instantiatedReferenceLazyMembers.ts(47,11): error TS2430: Interface 'Wrap<T>' incorrectly extends interface 'T'.
'Wrap<T>' is assignable to the constraint of type 'T', but 'T' could be instantiated with a different subtype of constraint '{ a?: string | undefined; }'.
instantiatedReferenceLazyMembers.ts(48,7): error TS2741: Property 'b' is missing in type '{ other: number; }' but required in type 'Wrap<{ a?: string | undefined; b: number; }>'.
instantiatedReferenceLazyMembers.ts(54,7): error TS2322: Type '<U>(x: U, y: string) => U' is not assignable to type 'number'.
instantiatedReferenceLazyMembers.ts(56,7): error TS2322: Type '(x: unknown, y: string) => unknown' is not assignable to type 'number'.


==== instantiatedReferenceLazyMembers.ts (10 errors) ====
// Member lookups and shape queries on instantiated class and interface
// references, including base types whose shape depends on the instantiation.

interface Base<T> {
value: T;
shared: string;
}
interface Derived<T> extends Base<T[]> {
shared: "derived";
}
declare const derived: Derived<number>;
const derived1 = derived.value;
const derived2 = derived.shared;
derived.missing;
~~~~~~~
!!! error TS2339: Property 'missing' does not exist on type 'Derived<number>'.

class Box<T> {
private secret!: T;
contents!: T;
}
declare const box: Box<string>;
const box1 = box.contents;
box.secret;
~~~~~~
!!! error TS2341: Property 'secret' is private and only accessible within class 'Box<T>'.

// Tagged<"b"> reduces to never, Tagged<"a"> doesn't.
type Tagged<T> = { kind: T } & { kind: "a" };
declare const other: { other: number };

interface Weak<T extends string> extends Tagged<T> {
opt?: number;
}
const weak1: Weak<"b"> = other;
~~~~~
!!! error TS2559: Type '{ other: number; }' has no properties in common with type 'Weak<"b">'.
const weak2: Weak<"a"> = other;
~~~~~
!!! error TS2741: Property 'kind' is missing in type '{ other: number; }' but required in type 'Weak<"a">'.
!!! related TS2728 instantiatedReferenceLazyMembers.ts:25:20: 'kind' is declared here.

type Callable<T> = { (): void; kind: T } & { kind: "a" };
interface Fn<T extends string> extends Callable<T> {}
declare const neverFn: Fn<"b">;
neverFn.bind;
~~~~
!!! error TS2339: Property 'bind' does not exist on type 'Fn<"b">'.
declare const fn: Fn<"a">;
const fn1 = fn.bind;

interface Dict<T extends string> extends Tagged<T> {
[key: string]: unknown;
}
declare const dict: Dict<"b">;
const dict1: { [key: string]: number } = dict;
~~~~~
!!! error TS2322: Type 'Dict<"b">' is not assignable to type '{ [key: string]: number; }'.
!!! error TS2322: 'string' index signatures are incompatible.
!!! error TS2322: Type 'unknown' is not assignable to type 'number'.

interface Wrap<T extends { a?: string }> extends T {}
~~~~
!!! error TS2430: Interface 'Wrap<T>' incorrectly extends interface 'T'.
!!! error TS2430: 'Wrap<T>' is assignable to the constraint of type 'T', but 'T' could be instantiated with a different subtype of constraint '{ a?: string | undefined; }'.
const wrap1: Wrap<{ a?: string; b: number }> = other;
~~~~~
!!! error TS2741: Property 'b' is missing in type '{ other: number; }' but required in type 'Wrap<{ a?: string | undefined; b: number; }>'.
!!! related TS2728 instantiatedReferenceLazyMembers.ts:48:33: 'b' is declared here.

type Two<T> = { <U>(x: U, y: T): U } & { <U>(x: U, y: string): U };
interface Overloads<T> extends Two<T> {}
declare function pipe<A extends any[], B>(f: (...args: A) => B): (...args: A) => B;
declare const merged: Overloads<string>;
const piped1: number = pipe(merged);
~~~~~~
!!! error TS2322: Type '<U>(x: U, y: string) => U' is not assignable to type 'number'.
declare const distinct: Overloads<number>;
const piped2: number = pipe(distinct);
~~~~~~
!!! error TS2322: Type '(x: unknown, y: string) => unknown' is not assignable to type 'number'.

interface Tree<T> extends Array<Tree<T>> {
value: T;
}
declare const tree: Tree<string>;
const tree1 = tree.map(child => child.value);

interface CallableBox<T> {
(): T;
}
declare const boxOrCallable: CallableBox<string> | Box<string>;
if (typeof boxOrCallable === "function") {
boxOrCallable;
}

259 changes: 259 additions & 0 deletions tsc/testdata/baselines/reference/compiler/instantiatedReferenceLazyMembers.symbols
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@@ -0,0 +1,259 @@
//// [tests/cases/compiler/instantiatedReferenceLazyMembers.ts] ////

=== instantiatedReferenceLazyMembers.ts ===
// Member lookups and shape queries on instantiated class and interface
// references, including base types whose shape depends on the instantiation.

interface Base<T> {
>Base : Symbol(Base, Decl(instantiatedReferenceLazyMembers.ts, 0, 0))
>T : Symbol(T, Decl(instantiatedReferenceLazyMembers.ts, 3, 15))

value: T;
>value : Symbol(Base.value, Decl(instantiatedReferenceLazyMembers.ts, 3, 19))
>T : Symbol(T, Decl(instantiatedReferenceLazyMembers.ts, 3, 15))

shared: string;
>shared : Symbol(Base.shared, Decl(instantiatedReferenceLazyMembers.ts, 4, 13))
}
interface Derived<T> extends Base<T[]> {
>Derived : Symbol(Derived, Decl(instantiatedReferenceLazyMembers.ts, 6, 1))
>T : Symbol(T, Decl(instantiatedReferenceLazyMembers.ts, 7, 18))
>Base : Symbol(Base, Decl(instantiatedReferenceLazyMembers.ts, 0, 0))
>T : Symbol(T, Decl(instantiatedReferenceLazyMembers.ts, 7, 18))

shared: "derived";
>shared : Symbol(Derived.shared, Decl(instantiatedReferenceLazyMembers.ts, 7, 40))
}
declare const derived: Derived<number>;
>derived : Symbol(derived, Decl(instantiatedReferenceLazyMembers.ts, 10, 13))
>Derived : Symbol(Derived, Decl(instantiatedReferenceLazyMembers.ts, 6, 1))

const derived1 = derived.value;
>derived1 : Symbol(derived1, Decl(instantiatedReferenceLazyMembers.ts, 11, 5))
>derived.value : Symbol(Base.value, Decl(instantiatedReferenceLazyMembers.ts, 3, 19))
>derived : Symbol(derived, Decl(instantiatedReferenceLazyMembers.ts, 10, 13))
>value : Symbol(Base.value, Decl(instantiatedReferenceLazyMembers.ts, 3, 19))

const derived2 = derived.shared;
>derived2 : Symbol(derived2, Decl(instantiatedReferenceLazyMembers.ts, 12, 5))
>derived.shared : Symbol(Derived.shared, Decl(instantiatedReferenceLazyMembers.ts, 7, 40))
>derived : Symbol(derived, Decl(instantiatedReferenceLazyMembers.ts, 10, 13))
>shared : Symbol(Derived.shared, Decl(instantiatedReferenceLazyMembers.ts, 7, 40))

derived.missing;
>derived : Symbol(derived, Decl(instantiatedReferenceLazyMembers.ts, 10, 13))

class Box<T> {
>Box : Symbol(Box, Decl(instantiatedReferenceLazyMembers.ts, 13, 16))
>T : Symbol(T, Decl(instantiatedReferenceLazyMembers.ts, 15, 10))

private secret!: T;
>secret : Symbol(Box.secret, Decl(instantiatedReferenceLazyMembers.ts, 15, 14))
>T : Symbol(T, Decl(instantiatedReferenceLazyMembers.ts, 15, 10))

contents!: T;
>contents : Symbol(Box.contents, Decl(instantiatedReferenceLazyMembers.ts, 16, 23))
>T : Symbol(T, Decl(instantiatedReferenceLazyMembers.ts, 15, 10))
}
declare const box: Box<string>;
>box : Symbol(box, Decl(instantiatedReferenceLazyMembers.ts, 19, 13))
>Box : Symbol(Box, Decl(instantiatedReferenceLazyMembers.ts, 13, 16))

const box1 = box.contents;
>box1 : Symbol(box1, Decl(instantiatedReferenceLazyMembers.ts, 20, 5))
>box.contents : Symbol(Box.contents, Decl(instantiatedReferenceLazyMembers.ts, 16, 23))
>box : Symbol(box, Decl(instantiatedReferenceLazyMembers.ts, 19, 13))
>contents : Symbol(Box.contents, Decl(instantiatedReferenceLazyMembers.ts, 16, 23))

box.secret;
>box.secret : Symbol(Box.secret, Decl(instantiatedReferenceLazyMembers.ts, 15, 14))
>box : Symbol(box, Decl(instantiatedReferenceLazyMembers.ts, 19, 13))
>secret : Symbol(Box.secret, Decl(instantiatedReferenceLazyMembers.ts, 15, 14))

// Tagged<"b"> reduces to never, Tagged<"a"> doesn't.
type Tagged<T> = { kind: T } & { kind: "a" };
>Tagged : Symbol(Tagged, Decl(instantiatedReferenceLazyMembers.ts, 21, 11))
>T : Symbol(T, Decl(instantiatedReferenceLazyMembers.ts, 24, 12))
>kind : Symbol(kind, Decl(instantiatedReferenceLazyMembers.ts, 24, 18))
>T : Symbol(T, Decl(instantiatedReferenceLazyMembers.ts, 24, 12))
>kind : Symbol(kind, Decl(instantiatedReferenceLazyMembers.ts, 24, 32))

declare const other: { other: number };
>other : Symbol(other, Decl(instantiatedReferenceLazyMembers.ts, 25, 13))
>other : Symbol(other, Decl(instantiatedReferenceLazyMembers.ts, 25, 22))

interface Weak<T extends string> extends Tagged<T> {
>Weak : Symbol(Weak, Decl(instantiatedReferenceLazyMembers.ts, 25, 39))
>T : Symbol(T, Decl(instantiatedReferenceLazyMembers.ts, 27, 15))
>Tagged : Symbol(Tagged, Decl(instantiatedReferenceLazyMembers.ts, 21, 11))
>T : Symbol(T, Decl(instantiatedReferenceLazyMembers.ts, 27, 15))

opt?: number;
>opt : Symbol(Weak.opt, Decl(instantiatedReferenceLazyMembers.ts, 27, 52))
}
const weak1: Weak<"b"> = other;
>weak1 : Symbol(weak1, Decl(instantiatedReferenceLazyMembers.ts, 30, 5))
>Weak : Symbol(Weak, Decl(instantiatedReferenceLazyMembers.ts, 25, 39))
>other : Symbol(other, Decl(instantiatedReferenceLazyMembers.ts, 25, 13))

const weak2: Weak<"a"> = other;
>weak2 : Symbol(weak2, Decl(instantiatedReferenceLazyMembers.ts, 31, 5))
>Weak : Symbol(Weak, Decl(instantiatedReferenceLazyMembers.ts, 25, 39))
>other : Symbol(other, Decl(instantiatedReferenceLazyMembers.ts, 25, 13))

type Callable<T> = { (): void; kind: T } & { kind: "a" };
>Callable : Symbol(Callable, Decl(instantiatedReferenceLazyMembers.ts, 31, 31))
>T : Symbol(T, Decl(instantiatedReferenceLazyMembers.ts, 33, 14))
>kind : Symbol(kind, Decl(instantiatedReferenceLazyMembers.ts, 33, 30))
>T : Symbol(T, Decl(instantiatedReferenceLazyMembers.ts, 33, 14))
>kind : Symbol(kind, Decl(instantiatedReferenceLazyMembers.ts, 33, 44))

interface Fn<T extends string> extends Callable<T> {}
>Fn : Symbol(Fn, Decl(instantiatedReferenceLazyMembers.ts, 33, 57))
>T : Symbol(T, Decl(instantiatedReferenceLazyMembers.ts, 34, 13))
>Callable : Symbol(Callable, Decl(instantiatedReferenceLazyMembers.ts, 31, 31))
>T : Symbol(T, Decl(instantiatedReferenceLazyMembers.ts, 34, 13))

declare const neverFn: Fn<"b">;
>neverFn : Symbol(neverFn, Decl(instantiatedReferenceLazyMembers.ts, 35, 13))
>Fn : Symbol(Fn, Decl(instantiatedReferenceLazyMembers.ts, 33, 57))

neverFn.bind;
>neverFn : Symbol(neverFn, Decl(instantiatedReferenceLazyMembers.ts, 35, 13))

declare const fn: Fn<"a">;
>fn : Symbol(fn, Decl(instantiatedReferenceLazyMembers.ts, 37, 13))
>Fn : Symbol(Fn, Decl(instantiatedReferenceLazyMembers.ts, 33, 57))

const fn1 = fn.bind;
>fn1 : Symbol(fn1, Decl(instantiatedReferenceLazyMembers.ts, 38, 5))
>fn.bind : Symbol(CallableFunction.bind, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --))
>fn : Symbol(fn, Decl(instantiatedReferenceLazyMembers.ts, 37, 13))
>bind : Symbol(CallableFunction.bind, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --))

interface Dict<T extends string> extends Tagged<T> {
>Dict : Symbol(Dict, Decl(instantiatedReferenceLazyMembers.ts, 38, 20))
>T : Symbol(T, Decl(instantiatedReferenceLazyMembers.ts, 40, 15))
>Tagged : Symbol(Tagged, Decl(instantiatedReferenceLazyMembers.ts, 21, 11))
>T : Symbol(T, Decl(instantiatedReferenceLazyMembers.ts, 40, 15))

[key: string]: unknown;
>key : Symbol(key, Decl(instantiatedReferenceLazyMembers.ts, 41, 5))
}
declare const dict: Dict<"b">;
>dict : Symbol(dict, Decl(instantiatedReferenceLazyMembers.ts, 43, 13))
>Dict : Symbol(Dict, Decl(instantiatedReferenceLazyMembers.ts, 38, 20))

const dict1: { [key: string]: number } = dict;
>dict1 : Symbol(dict1, Decl(instantiatedReferenceLazyMembers.ts, 44, 5))
>key : Symbol(key, Decl(instantiatedReferenceLazyMembers.ts, 44, 16))
>dict : Symbol(dict, Decl(instantiatedReferenceLazyMembers.ts, 43, 13))

interface Wrap<T extends { a?: string }> extends T {}
>Wrap : Symbol(Wrap, Decl(instantiatedReferenceLazyMembers.ts, 44, 46))
>T : Symbol(T, Decl(instantiatedReferenceLazyMembers.ts, 46, 15))
>a : Symbol(a, Decl(instantiatedReferenceLazyMembers.ts, 46, 26))
>T : Symbol(T, Decl(instantiatedReferenceLazyMembers.ts, 46, 15))

const wrap1: Wrap<{ a?: string; b: number }> = other;
>wrap1 : Symbol(wrap1, Decl(instantiatedReferenceLazyMembers.ts, 47, 5))
>Wrap : Symbol(Wrap, Decl(instantiatedReferenceLazyMembers.ts, 44, 46))
>a : Symbol(a, Decl(instantiatedReferenceLazyMembers.ts, 47, 19))
>b : Symbol(b, Decl(instantiatedReferenceLazyMembers.ts, 47, 31))
>other : Symbol(other, Decl(instantiatedReferenceLazyMembers.ts, 25, 13))

type Two<T> = { <U>(x: U, y: T): U } & { <U>(x: U, y: string): U };
>Two : Symbol(Two, Decl(instantiatedReferenceLazyMembers.ts, 47, 53))
>T : Symbol(T, Decl(instantiatedReferenceLazyMembers.ts, 49, 9))
>U : Symbol(U, Decl(instantiatedReferenceLazyMembers.ts, 49, 17))
>x : Symbol(x, Decl(instantiatedReferenceLazyMembers.ts, 49, 20))
>U : Symbol(U, Decl(instantiatedReferenceLazyMembers.ts, 49, 17))
>y : Symbol(y, Decl(instantiatedReferenceLazyMembers.ts, 49, 25))
>T : Symbol(T, Decl(instantiatedReferenceLazyMembers.ts, 49, 9))
>U : Symbol(U, Decl(instantiatedReferenceLazyMembers.ts, 49, 17))
>U : Symbol(U, Decl(instantiatedReferenceLazyMembers.ts, 49, 42))
>x : Symbol(x, Decl(instantiatedReferenceLazyMembers.ts, 49, 45))
>U : Symbol(U, Decl(instantiatedReferenceLazyMembers.ts, 49, 42))
>y : Symbol(y, Decl(instantiatedReferenceLazyMembers.ts, 49, 50))
>U : Symbol(U, Decl(instantiatedReferenceLazyMembers.ts, 49, 42))

interface Overloads<T> extends Two<T> {}
>Overloads : Symbol(Overloads, Decl(instantiatedReferenceLazyMembers.ts, 49, 67))
>T : Symbol(T, Decl(instantiatedReferenceLazyMembers.ts, 50, 20))
>Two : Symbol(Two, Decl(instantiatedReferenceLazyMembers.ts, 47, 53))
>T : Symbol(T, Decl(instantiatedReferenceLazyMembers.ts, 50, 20))

declare function pipe<A extends any[], B>(f: (...args: A) => B): (...args: A) => B;
>pipe : Symbol(pipe, Decl(instantiatedReferenceLazyMembers.ts, 50, 40))
>A : Symbol(A, Decl(instantiatedReferenceLazyMembers.ts, 51, 22))
>B : Symbol(B, Decl(instantiatedReferenceLazyMembers.ts, 51, 38))
>f : Symbol(f, Decl(instantiatedReferenceLazyMembers.ts, 51, 42))
>args : Symbol(args, Decl(instantiatedReferenceLazyMembers.ts, 51, 46))
>A : Symbol(A, Decl(instantiatedReferenceLazyMembers.ts, 51, 22))
>B : Symbol(B, Decl(instantiatedReferenceLazyMembers.ts, 51, 38))
>args : Symbol(args, Decl(instantiatedReferenceLazyMembers.ts, 51, 66))
>A : Symbol(A, Decl(instantiatedReferenceLazyMembers.ts, 51, 22))
>B : Symbol(B, Decl(instantiatedReferenceLazyMembers.ts, 51, 38))

declare const merged: Overloads<string>;
>merged : Symbol(merged, Decl(instantiatedReferenceLazyMembers.ts, 52, 13))
>Overloads : Symbol(Overloads, Decl(instantiatedReferenceLazyMembers.ts, 49, 67))

const piped1: number = pipe(merged);
>piped1 : Symbol(piped1, Decl(instantiatedReferenceLazyMembers.ts, 53, 5))
>pipe : Symbol(pipe, Decl(instantiatedReferenceLazyMembers.ts, 50, 40))
>merged : Symbol(merged, Decl(instantiatedReferenceLazyMembers.ts, 52, 13))

declare const distinct: Overloads<number>;
>distinct : Symbol(distinct, Decl(instantiatedReferenceLazyMembers.ts, 54, 13))
>Overloads : Symbol(Overloads, Decl(instantiatedReferenceLazyMembers.ts, 49, 67))

const piped2: number = pipe(distinct);
>piped2 : Symbol(piped2, Decl(instantiatedReferenceLazyMembers.ts, 55, 5))
>pipe : Symbol(pipe, Decl(instantiatedReferenceLazyMembers.ts, 50, 40))
>distinct : Symbol(distinct, Decl(instantiatedReferenceLazyMembers.ts, 54, 13))

interface Tree<T> extends Array<Tree<T>> {
>Tree : Symbol(Tree, Decl(instantiatedReferenceLazyMembers.ts, 55, 38))
>T : Symbol(T, Decl(instantiatedReferenceLazyMembers.ts, 57, 15))
>Array : Symbol(Array, Decl(lib.es5.d.ts, --, --), Decl(lib.es5.d.ts, --, --), Decl(lib.es2015.core.d.ts, --, --), Decl(lib.es2015.iterable.d.ts, --, --), Decl(lib.es2015.symbol.wellknown.d.ts, --, --) ... and 4 more)
>Tree : Symbol(Tree, Decl(instantiatedReferenceLazyMembers.ts, 55, 38))
>T : Symbol(T, Decl(instantiatedReferenceLazyMembers.ts, 57, 15))

value: T;
>value : Symbol(Tree.value, Decl(instantiatedReferenceLazyMembers.ts, 57, 42))
>T : Symbol(T, Decl(instantiatedReferenceLazyMembers.ts, 57, 15))
}
declare const tree: Tree<string>;
>tree : Symbol(tree, Decl(instantiatedReferenceLazyMembers.ts, 60, 13))
>Tree : Symbol(Tree, Decl(instantiatedReferenceLazyMembers.ts, 55, 38))

const tree1 = tree.map(child => child.value);
>tree1 : Symbol(tree1, Decl(instantiatedReferenceLazyMembers.ts, 61, 5))
>tree.map : Symbol(Array.map, Decl(lib.es5.d.ts, --, --))
>tree : Symbol(tree, Decl(instantiatedReferenceLazyMembers.ts, 60, 13))
>map : Symbol(Array.map, Decl(lib.es5.d.ts, --, --))
>child : Symbol(child, Decl(instantiatedReferenceLazyMembers.ts, 61, 23))
>child.value : Symbol(Tree.value, Decl(instantiatedReferenceLazyMembers.ts, 57, 42))
>child : Symbol(child, Decl(instantiatedReferenceLazyMembers.ts, 61, 23))
>value : Symbol(Tree.value, Decl(instantiatedReferenceLazyMembers.ts, 57, 42))

interface CallableBox<T> {
>CallableBox : Symbol(CallableBox, Decl(instantiatedReferenceLazyMembers.ts, 61, 45))
>T : Symbol(T, Decl(instantiatedReferenceLazyMembers.ts, 63, 22))

(): T;
>T : Symbol(T, Decl(instantiatedReferenceLazyMembers.ts, 63, 22))
}
declare const boxOrCallable: CallableBox<string> | Box<string>;
>boxOrCallable : Symbol(boxOrCallable, Decl(instantiatedReferenceLazyMembers.ts, 66, 13))
>CallableBox : Symbol(CallableBox, Decl(instantiatedReferenceLazyMembers.ts, 61, 45))
>Box : Symbol(Box, Decl(instantiatedReferenceLazyMembers.ts, 13, 16))

if (typeof boxOrCallable === "function") {
>boxOrCallable : Symbol(boxOrCallable, Decl(instantiatedReferenceLazyMembers.ts, 66, 13))

boxOrCallable;
>boxOrCallable : Symbol(boxOrCallable, Decl(instantiatedReferenceLazyMembers.ts, 66, 13))
}

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