Why does NSPredicate(format: "age > %@", 18) sometimes fail silently when filtering an array of dictionaries?

hard📝 Conceptual Q10 of 15

iOS Swift - Local Data Persistence

Why does NSPredicate(format: "age > %@", 18) sometimes fail silently when filtering an array of dictionaries?

ABecause %@ expects an object, but 18 is a primitive Int, causing a type mismatch

BBecause NSPredicate cannot filter dictionaries

CBecause the format string must use %d for numbers

DBecause the key "age" must be a string, not a number

Step-by-Step Solution

Solution:

Step 1: Understand %@ placeholder usage
%@ expects an object like NSNumber, not a primitive Int.
Step 2: Recognize silent failure cause
Passing Int directly causes type mismatch, so predicate fails silently.
Final Answer:
Because %@ expects an object, but 18 is a primitive Int, causing a type mismatch -> Option A
Quick Check:
Use NSNumber or %d for numeric values in NSPredicate [OK]

Quick Trick: Use NSNumber or %d for numbers in NSPredicate format [OK]

Common Mistakes:

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