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fix(ts-lens): Have the fallback dictate type #2

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Dec 19, 2017
Merged

fix(ts-lens): Have the fallback dictate type #2

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20 changes: 14 additions & 6 deletions src/lens.ts
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Original file line number Diff line number Diff line change
@@ -1,10 +1,15 @@
const getKey = <T, Key extends keyof T>(key: Key) => (value: T): T[Key] =>
value && value[key];

const getOrKey = <T, Key extends keyof T, OrValue>(
const getOrKey = <T, Key extends keyof T, OrValue extends T[Key]>(
key: Key,
orValue: OrValue & T[Key]
) => (value: T): T[Key] => (value && value[key]) || orValue;
orValue: OrValue
) => (value: T): OrValue => {
if (value && value.hasOwnProperty(key)) {
return (value && value[key]) as any;
}
return orValue;
};

const setKey = <T, Key extends keyof T>(key: Key, setValue: T[Key]) => (
value: T
Expand Down Expand Up @@ -62,10 +67,13 @@ export class Lens<A extends {}, B> {
/** Like thenKey but now we have a default
* Ex: Get a value in a model dictionary or return the default
*/
public thenKeyOr<Key extends keyof B, C>(key: Key, defaultValue: C & B[Key]) {
public thenKeyOr<Key extends keyof B, C extends B[Key]>(
key: Key,
defaultValue: C
) {
return this.then(
new Lens(getOrKey(key, defaultValue), (value: C & B[Key]) =>
setKey<B, Key>(key, value)
new Lens<B, C>(getOrKey(key, defaultValue), (value: C) =>
setKey<B, Key>(key, value as any)
)
);
}
Expand Down