Autosave: 2023-04-06 19:24:50

Programming_Languages/TypeScript/Generics.md

@@ -127,3 +127,33 @@ console.log(allItems);
 //   { key: 2, value: "two" }
 // ]
 ```
+
+## Real examples
+
+### GraphQL client for query and mutation requests over `fetch`
+
+### VSCode extension TreeView generator
+
+In VSCode a TreeView is a list of values that may have nested values, like a directory. The following generic is a helper function that generates a TreeView based on a given class that is passed in as an argument, along with the class's constructor values (`args` in the example). It also calls a method `refresh` on each instance of the class.
+
+```ts
+function createTreeView<
+  T extends IndexHyperlinksProvider | IndexMetadataProvider,
+  U extends LinkTypes | MetadataTypes
+>(
+  viewType: string,
+  ProviderClass: new (...args: any[]) => T,
+  type: U,
+  activeEditor?: string | undefined,
+  ...args: ConstructorParameters<typeof ProviderClass>
+): T {
+  const view = new ProviderClass(...args, type);
+  if (view instanceof IndexHyperlinksProvider) {
+    view.refresh(activeEditor, type as LinkTypes);
+  } else if (view instanceof IndexMetadataProvider) {
+    view.refreshIndex();
+  }
+  vscode.window.registerTreeDataProvider(viewType, view);
+  return view;
+}
+```

Programming_Languages/TypeScript/Mapped_types.md

@@ -0,0 +1,130 @@
+---
+categories:
+  - Programming Languages
+tags:
+  - typescript
+---
+
+# Mapped types in TypeScript
+
+A mapped type is a way to create new types based on existing ones by transforming their properties
+
+As it works on a single type and typically narrows or limits the properties it works in a way that is opposite to a [union]() or [intersection]() type.
+
+> Mapped types are an example of when `type` is preferable to `interface`, since you cannot generate mapped types as interfaces, although you may generate a mapped type from an interface.
+
+For the demonstrations we will use the following type as the example that we will map from:
+
+```ts
+type Person = {
+  name: string;
+  age: number;
+  city: string;
+  country: string;
+};
+```
+
+### Read only mapped type
+
+Creates a type with all properties of the given type set to `readonly`:
+
+```ts
+type Readonly<T> = {
+  readonly [P in keyof T]: T[P];
+};
+
+type ReadonlyPerson = Readonly<Person>;
+```
+
+This is equivalent to:
+
+```ts
+type ReadonlyPerson = {
+  readonly name: string;
+  readonly age: number;
+  readonly city: string;
+  readonly country: string;
+};
+```
+
+### Partial mapped type
+
+Creates a type with all properties of the given type set to optional.
+
+```ts
+type Partial<T> = {
+  [P in keyof T]?: T[P];
+};
+
+type PartialPerson = Partial<Person>;
+```
+
+This is equivalent to:
+
+```ts
+type PartialPerson = {
+  name?: string;
+  age?: number;
+  city?: string;
+  country?: string;
+};
+```
+
+### Pick mapped type
+
+```ts
+type Pick<T, K extends keyof T> = {
+  [P in K]: T[P];
+};
+
+type PersonNameAndAge = Pick<Person, "name" | "age">;
+```
+
+This is equivalent to:
+
+```ts
+type PersonNameAndAge = {
+  name: string;
+  age: number;
+};
+```
+
+### Record mapped type
+
+Creates a type with keys of the given type and values of the specified type.
+
+> How does this related to `Record` more generally in TS?
+
+> How is this different from `Pick` ?
+
+```ts
+type Record<K extends keyof any, T> = {
+  [P in K]: T;
+};
+
+type PersonRecord = Record<"id", Person>;
+```
+
+This is equivalent to:
+
+```ts
+type PersonRecord = {
+  id: Person;
+};
+```
+
+### Exclude mapped type
+
+Creates a type by excluding specific properties from the given type.
+
+```ts
+type Exclude<T, U> = T extends U ? never : T;
+
+type KeysWithoutAge = Exclude<keyof Person, "age">;
+```
+
+This is equivalent to:
+
+```ts
+type KeysWithoutAge = "name" | "city" | "country";
+```

_meta/Resources.md

@@ -104,7 +104,7 @@ J. Hunt. 2019. **An Advanced Guide to Python Programming**
 
 [Learning Arduino with Python](https://realpython.com/arduino-python/)
 
-[Python Programming Projects](https://github.com/zhiwehu/Python-programming-exercises/blob/master/100%2B%20Python%20challenging%20programming%20exercises.txt)
+[Python Programming Exercises](https://github.com/zhiwehu/Python-programming-exercises/blob/master/100%2B%20Python%20challenging%20programming%20exercises.txt)
 
 ## Shell