storage_write_without_read

Default Severity	Category
warn	StorageOperations

What it does

Flags storage writes (.set()) on a storage object when the same key is never read back with .get() or checked with .has() — indicating a write whose value is never used.

Why is this bad

Performing a storage write without reading the value first wastes Soroban storage write fees for data that's never used. Each unnecessary write consumes CPU and memory budget, adding cost without benefit.

Example

Bad — writing a value that is never read wastes storage write fees:

// ❌ Triggers: storage_write_without_read
fn update(env: Env, key: &str) {
    env.storage().instance().set(key, &1);
    // The value at `key` is never read back
}

Good — read the value back if you intend to use it:

// ✅ Fixed: read before write
fn update(env: Env, key: &str) {
    let _existing: Option<i32> = env.storage().instance().get(key);
    env.storage().instance().set(key, &1);
}

Suggested Fix

Either add a corresponding .get() or .has() call on the same storage object with the same key before the write, or remove the unnecessary write altogether.

Cost Impact

• Ledger entry accesses & I/O bytes: Unnecessary storage writes consume ledger entry write slots, write I/O bytes, and incur rent and state expansion fees without providing any functional benefit.