map_insert_in_loop

Default Severity	Category
warn	Compute

What it does

Flags Map::insert calls executed inside loop bodies.

Why is this bad

Inserting elements into a Soroban Map inside a loop repeatedly invokes host object mutation and re-allocations per iteration, driving up CPU costs.

Example

Bad — inserting into a map inside a loop:

// ❌ Triggers: map_insert_in_loop
let mut map = Map::new(&env);
for (k, v) in &items {
    map.set(*k, *v);
}

Good — populate or construct the map outside or via batch initialization:

// ✅ Fixed: construct map outside loop or batch insertions
let mut map = Map::new(&env);
// Populate items...

Suggested Fix

Avoid calling .set() or .insert() on host maps inside loop iterations where possible. Pre-populate or aggregate outside the loop.

Cost Impact

• CPU instructions: Repeated host map insertions incur continuous host function dispatch overhead and entry reallocation costs, significantly inflating CPU instruction consumption.