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06_complex/infer.ts

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+const arr = [1, 2, '3', 4, 5];
+// get type of array
+type GetArrItem<Arg> = Arg extends (infer Item)[] ? Item : never;
+
+type ArrItem = GetArrItem<typeof arr>
+
+const user = { name: 'John', age: 30 } as const;
+// get type of name property
+type GetObjectNameType<Name> = Name extends { name: infer T } ? T : never
+
+type UserName = GetObjectNameType<typeof user>
+
+const double = (x: number, s: 'foo') => x * 2;
+// get type of first argument of function
+type GetFirstFuncArg<Arg> = Arg extends (a, x: infer T) => any ? T : never;
+
+type DoubleArgType = GetFirstFuncArg<typeof double>