go.map_without_size_hint

Performance Low

Detects map initialization without capacity hint when the expected size is known.

Why It Matters

Maps without size hints:

• Repeated rehashing — Map grows and rehashes as items added
• Memory copying — Each grow copies all entries
• Fragmented memory — Multiple allocations instead of one

Example

// ❌ Before (no hint)
result := make(map[string]int)
for _, item := range items {
    result[item.Key] = item.Value
}

// ✅ After (with hint)
result := make(map[string]int, len(items))
for _, item := range items {
    result[item.Key] = item.Value
}

What Unfault Detects

• make(map[K]V) in loops where size is known
• Map initialization followed by loop filling it

Auto-Fix

Unfault adds size hints:

result := make(map[string]int, len(items))

Related Rules

• go.slice_append_in_loop