and I think we're good!

Author: Harris-Miller

test/assoc.test.ts

@@ -13,6 +13,7 @@ const obj: BasicObj = { str: 'foo', num: 1 };
 //
 
 // assoc(key)(__, obj)(val)
+expectError(assoc(__));
 expectType<BasicObj>(assoc('str')(__, obj)('bar'));
 expectType<Omit<BasicObj, 'str'> & Record<'str', number>>(assoc('str')(__, obj)(2));
 expectType<Omit<{ other: string }, 'str'> & Record<'str', string>>(assoc('str')(__, {} as { other: string })('foo'));
@@ -61,7 +62,7 @@ expectType<Omit<{ other: string }, 'str'> & Record<'str', string>>(assoc('str',
 //
 
 // assoc(__, __, obj)(key)(val)
-expectError(assoc(__, __, obj)(__)('bar'));
+expectError(assoc(__, __, obj)(__));
 expectType<BasicObj>(assoc(__, __, obj)('str')('bar'));
 expectType<Omit<BasicObj, 'str'> & Record<'str', number>>(assoc(__, __, obj)('str')(2));
 expectType<Omit<{ other: string }, 'str'> & Record<'str', string>>(assoc(__, __, {} as { other: string })('str')('bar'));
@@ -75,3 +76,23 @@ expectType<Omit<{ other: string }, 'str'> & Record<'str', string>>(assoc(__, __,
 expectType<BasicObj>(assoc(__, __, obj)('str', 'bar'));
 expectType<Omit<BasicObj, 'str'> & Record<'str', number>>(assoc(__, __, obj)('str', 2));
 expectType<Omit<{ other: string }, 'str'> & Record<'str', string>>(assoc(__, __, {} as { other: string })('str', 'bar'));
+
+//
+// rest
+//
+
+// assoc(__, val, obj)(prop)
+expectError(assoc(__,'bar', obj)(__));
+expectType<BasicObj>(assoc(__,'bar', obj)('str'));
+expectType<Omit<BasicObj, 'str'> & Record<'str', number>>(assoc(__, 2, obj)('str'));
+expectType<Omit<{ other: string }, 'str'> & Record<'str', string>>(assoc(__, 'bar', {} as { other: string })('str'));
+
+// assoc(key, __, obj)(__, val)
+expectType<BasicObj>(assoc('str', __, obj)('bar'));
+expectType<Omit<BasicObj, 'str'> & Record<'str', number>>(assoc('str', __, obj)(2));
+expectType<Omit<{ other: string }, 'str'> & Record<'str', string>>(assoc('str', __, {} as { other: string })('bar'));
+
+// assoc(key, val, obj)
+expectType<BasicObj>(assoc('str', 'bar', obj));
+expectType<Omit<BasicObj, 'str'> & Record<'str', number>>(assoc('str', 2, obj));
+expectType<Omit<{ other: string }, 'str'> & Record<'str', string>>(assoc('str', 'foo', {} as { other: string }));

types/assoc.d.ts

@@ -1,7 +1,7 @@
 import { Placeholder, AssocResults } from './util/tools';
 
 // assoc(prop)
-export function assoc<K extends PropertyKey>(prop: K): {
+export function assoc<K extends PropertyKey>(prop: K extends Placeholder ? never : K): {
   // assoc(prop)(val)
   <T>(val: T): {
     // assoc(prop)(val)(obj), when obj has key prop, tests if val is typeof obj[prop] for best return type
@@ -38,7 +38,7 @@ export function assoc<T>(__: Placeholder, val: T) : {
 
 // assoc(prop, val)
 export function assoc<K extends PropertyKey, T>(prop: K extends Placeholder ? never : K, val: T): {
-  // assoc(prop, val)(obj), when obj has key prop, tests if val is typeof obj[prop] for best return type
+  // assoc(prop, val)(obj)
   <U>(obj: U): AssocResults<K, T, U>;
 };
 
@@ -54,15 +54,11 @@ export function assoc<U>(__: Placeholder, __2: Placeholder, obj: U): {
   <K extends PropertyKey, T>(prop: K, val: T): AssocResults<K, T, U>;
 };
 
-// assoc(prop, __, obj)(val), when prop is not keyof obj
-export function assoc<K extends PropertyKey, U>(prop: K extends Placeholder ? never : K, __: Placeholder, obj: U): <T>(val: T) => U & Record<K, T>;
-// assoc(prop, __, obj)(val), when K is keyof obj, tests if val is typeof obj[prop] for best return type
-export function assoc<K extends keyof U, U>(prop: K, __: Placeholder, obj: U): <T>(val: T) => T extends U[K] ? U : Omit<U, K> & Record<K, T>;
-// assoc(__, val, obj)(prop), this tests if prop is keyof obj and if val is typeof obj[prop] for best return type
-export function assoc<T, U>(__: Placeholder, val: T extends Placeholder ? never : T, obj: U): <K extends PropertyKey>(prop: K) => K extends keyof U ? T extends U[K] ? U : Omit<U, K> & Record<K, T> : U & Record<K, T>;
-// assoc(prop, val, obj) when prop is not keyof obj
-export function assoc<K extends PropertyKey, T, U>(prop: K extends Placeholder ? never : K, val: T extends Placeholder ? never : T, obj: U): U & Record<K, T>;
-// assoc(prop, val, obj) when prop is keyof obj  and val is not same type
-export function assoc<K extends keyof U, T, U>(prop: K, val: T extends Placeholder ? never : T, obj: U): Omit<U, K> & Record<K, T>;
-// assoc(prop, val, obj) when prop is keyof obj and val is same type
-export function assoc<K extends keyof U, U>(prop: K, val: U[K], obj: U): U;
+// assoc(__, val, obj)(prop)
+export function assoc<T, U>(__: Placeholder, val: T, obj: U): <K extends PropertyKey>(prop: K extends Placeholder ? never : K) => AssocResults<K, T, U>;
+
+// assoc(prop, __, obj)(val)
+export function assoc<K extends PropertyKey, U>(prop: K, __: Placeholder, obj: U): <T>(val: T) => AssocResults<K, T, U>;
+
+// assoc(prop, val, obj)
+export function assoc<K extends PropertyKey, T, U>(prop: K, val: T, obj: U): AssocResults<K, T, U>;