Object-Oriented Design

Tell, Don’t Ask: Keep Decisions with the Object That Owns the Data

Tell, Don’t Ask: Keep Decisions with the Object That Owns the Data A class can expose perfectly reasonable getters and still make a codebase harder to change. The trouble appears when callers fetch several values, interpret them, make a business decision, and then tell the object how to update itself. The data lives in one place, but the rule that gives the data meaning lives somewhere else. Tell, Don’t Ask is a design guideline for reducing that split. Instead of asking an object for internal state so a caller can decide what should happen, prefer telling the object the meaningful operation you want performed. The object can then apply the rules that belong with its state.