Core · Module 8 · Lesson 4 of 5

Project: Failing Library Operations Cleanly

Build a LibraryError hierarchy, validate a checkout before mutating, and commit with noexcept swaps so failures leave no residue.

ProAbout 12 minutes

By the end you can

Design a LibraryError hierarchy rooted in runtime_error
Validate checkout preconditions before mutating shared state
Commit loans with strong safety and centralized handling

Builds on Exception Safety: Guarantees and RAII Discipline.

01 · A question first

The desk tries to loan a missing book to an expired member with fines outstanding. Three checks fail at once, the log shows one vague line, and the shelf count is already decremented. Which error should the patron see, and how do you unwind the half-applied loan?

Make a guess before you read on.

02 · The idea

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What's inside

Why checkout concentrates every hazard
How a small hierarchy names each failure
Why staging makes failure residue impossible
What it costs and what to enforce
How to log a failure with context
Complete solution
Where it is used