Imperative – you instruct a machine what to do step by step. Example: assembly language.
Declarative – you instruct a machine what you want to get and it supposes to figure it how to do it. Example: SQL.
Imperative vs declarative is an example of limitation of categorical thinking. There is a spectrum of values, but we trapped with two categories.
Let’s take a look at some examples.
List operations (iteration, filtering etc) from most imperative to most declarative approach:
- Imperative programming, which includes
jumpin terms of modern assembly). For example assembly.
- Structured programming, which includes
forloops and indexed access to elements of the array. For example Pascal.
- Map/Reduce concept, which includes map and reduce operations, but abstracts away how list itself is organized. For example map/reduce in Scheme.
- Relational databases, which abstracts away all implementation details of storage. For example SQL.
CSS position models from most imperative to most declarative approach:
margin. You need to juggle those properties to achieve the desired layout. For example, see how to position div in the center.
- Flexbox. A lot of hacks went away, but you still can’t describe layout precisely, it is still some approximation
- CSS Grid Layout. You can describe the layout.
Also, need to notice that there is a way too much “knobs” in CSS to manipulate layout. See this video from deconstructconf to understand how this task can be solved better.