Conditional Types

Conditional types work like type-level if/else.

    ## Syntax
    ```ts
    T extends U ? X : Y
    ```
    
    ## Example
    
    ```ts
    type IsString<T> = T extends string ? true : false;
    
    type A = IsString<string>; // true
    type B = IsString<number>; // false
    ```
    
    ## Practical example
    
    ```ts
    type ApiResult<T> = T extends Error ? { ok: false } : { ok: true; data: T };
    ```
    
    ## Graph
    ```mermaid
    flowchart TD
      A[T] --> B{extends?}
      B -->|Yes| C[Type X]
      B -->|No| D[Type Y]
    ```
    
    ## Remember
    - Conditional types adapt APIs
    - Powerful for libraries