discarded_storage_read

Default Severity: warn

What it does

Detects reads from storage whose result is never used (e.g., bound to _, evaluated purely as a statement, or bound and never subsequently referenced).

Why is this bad?

{% hint style="danger" } Storage reads are among the most expensive operations available to a Soroban contract. Performing a read whose result is discarded is pure waste with no behavioral purpose, unnecessarily driving up resource metering and network fees.

Example

// ❌ Bad: storage read result is discarded
let _ = env.storage().instance().get::<u32, i32>(&key);
env.storage().persistent().get::<u32, i32>(&key); //~ WARNING

Suggested Fix

{% hint style="success" } Delete the storage read entirely if the state is not needed.

// ✅ Good: read omitted

Scope

• Flags get and has calls on Instance, Persistent, and Temporary storage where the returned value is unused.
• Deliberate existence checks where the result is consumed (e.g. if env.storage().persistent().has(&key), or matching on an Option read) are not flagged.