LLD 1
-----
- **What is the Lowest Level?**
- Code
- Not feasible to communicate at this level
- Large systems can have hundreds of thousands of LOC
- if the interviewer asks you to design amazon, he doesn't expect you to write code. He first expects the HLD/LLD
- **High Level Design**
- very high level view
- still allows you to see that there are some components and the way things operate
- **Low level design**
- closer look, but still higher than code.
- behavior / skeleton, not implementation
-- --
Example
-------
Website - webpage, application code, DB
Fetch data, persist
**HLD**
- 
- doesn't worry about how the data is fetched, what the DB schema is, what tables exist, what the tech stack is
**LLD**
- not the actual code. Higher level than code
- Consider a function that adds two numbers
```python
def add(a: int, b: int) -> int: ...
```
LLD just tells you that the function takes 2 args and returns the sum. Doesn't bother about the actual implementation
- LLD talks about entities (classes), their interactions, and their properties (attributes) and behavior (functions)
-- --
**Procedural Code**
- top-down
- no obvious segregation of responsibility
- no one-to-one mapping to real world entities
**Object Oriented**
- map any real world entity to a code entity (class)
- list down the properties/attributes of each entity
- list down the actions/behavior/methods of each entity
- list down the interactions b/w various entities
-- --
Example:
Template / Blueprint for a Bird
-------------------------------
```python
class Bird:
weight: float
height: float
color: Color
def fly(): ...
```
This template does not signify one particular bird. It describes a class of a Bird.
A specific bird will be represented by an instance of this class.
-- --
Constructing an instance / object
---------------------------------
- invoke the constructor of the class
-
- ```python
```