Angular Memoized Selectors: Optimizing Data Selection

Angular's selectors are powerful tools for deriving data from your store. However, repeated calls to the same selector with the same input can lead to unnecessary computations, especially in complex applications. This challenge asks you to implement memoized selectors in Angular, which cache the results of selector computations based on their inputs, significantly improving performance by avoiding redundant calculations.

Problem Description

You need to create a reusable MemoizedSelector utility that can be used to wrap existing Angular selectors, adding memoization functionality. The MemoizedSelector should take an existing selector function as input and return a new selector function that memoizes its results. The memoized selector should only re-compute the result when its inputs change.

Key Requirements:

• Memoization: The core functionality is to cache the result of the selector based on its input arguments.
• Equality Check: You must implement a mechanism to determine if the input arguments have changed. For simplicity, assume a deep equality check is sufficient.
• Reusability: The MemoizedSelector should be a generic utility that can be applied to any selector function.
• Immutability: The original selector function should not be modified. The MemoizedSelector should return a new selector function.
• TypeScript: The solution must be written in TypeScript.

Expected Behavior:

When the memoized selector is called with the same input arguments as a previous call, it should return the cached result without re-executing the original selector. When the input arguments change, the original selector should be executed, the result cached, and the new result returned.

Edge Cases to Consider:

• Selectors with no arguments.
• Selectors with complex object arguments.
• Performance implications of deep equality checks (consider potential optimizations if necessary, though this is not a primary focus).
• Handling of null or undefined input values.

Examples

Example 1:

Input:
selector: (state: { count: number }) => state.count + 1;
initialInput: { count: 10 };

Output:
11 (first call)
11 (subsequent calls with { count: 10 })
12 (call with { count: 11 })

Explanation: The selector adds 1 to the count property of the state. The first call with count: 10 returns 11 and caches it. Subsequent calls with the same input return the cached value 11. When count changes to 11, the selector is re-executed, returning 12 and updating the cache.

Example 2:

Input:
selector: (state: { user: { name: string, age: number } }) => `${state.user.name} is ${state.user.age} years old.`;
initialInput: { user: { name: "Alice", age: 30 } };

Output:
"Alice is 30 years old." (first call)
"Alice is 30 years old." (subsequent calls with { user: { name: "Alice", age: 30 } })
"Bob is 40 years old." (call with { user: { name: "Bob", age: 40 } })

Explanation: The selector constructs a string based on the user's name and age. Changes to either name or age trigger a re-computation and cache update.

Example 3: (Edge Case - No Arguments)

Input:
selector: (state: any) => "Hello";
initialInput: null;

Output:
"Hello" (first call)
"Hello" (subsequent calls)

Explanation: Even with no arguments, the memoization should still function correctly, caching the constant string "Hello".

Constraints

• The MemoizedSelector utility should be a function that accepts a selector function and an initial input, and returns a memoized selector function.
• The deep equality check should be reasonably efficient, but optimizing it is not the primary focus. A simple recursive comparison is acceptable.
• The solution must be written in TypeScript and adhere to good coding practices.
• The initial input is used only to initialize the cache. Subsequent calls can have different inputs.

Notes

• Consider using a simple object to store the cached results.
• The deep equality check can be implemented recursively.
• Think about how to handle the initial input and subsequent calls with different inputs.
• Focus on the core memoization logic; error handling and extensive testing are not required for this challenge.
• The initial input is only used to initialize the cache. Subsequent calls can have different inputs.