# exposed-0003: Table.clone — O(N²) repeated List allocation in property filter

**Severity:** MEDIUM
**File:** exposed-core/src/main/kotlin/org/jetbrains/exposed/v1/core/Table.kt
**Line:** 1686
**Status:** PATCHED

## Description

The private `T.clone()` utility in `Table` is used internally when cloning column objects (e.g., during
alias creation and column type mutation). It contains:

```kotlin
val allValues = memberProperties
    .filter { it in mutableProperties || it.name in consParams.map(KParameter::name) }
    .associate { it.name to (replaceArgs[it] ?: it.get(this@clone)) }
```

The predicate `it.name in consParams.map(KParameter::name)` is evaluated for every element of
`memberProperties`. Each evaluation calls `.map(KParameter::name)`, allocating a fresh `List<String?>`.
For a class with P properties and C constructor parameters, this is P × C string comparisons plus P list
allocations.

`Column` classes can have 10–20 properties; this is called once per column per alias/clone operation. In a
query with 50 aliased columns this function runs 50 times, each time performing up to 400 string comparisons
with 20 temporary `List` allocations per call — 20 000 comparisons and 1 000 heap allocations total.

## Root Cause

`consParams.map(KParameter::name)` is a lambda-captured expression inside the `.filter {}` predicate.
Kotlin does not hoist it; it runs inside the hot loop.

## Fix

Pre-compute the parameter name set once, outside the filter:

```kotlin
// Before (O(P×C) with P list allocations):
val allValues = memberProperties
    .filter { it in mutableProperties || it.name in consParams.map(KParameter::name) }
    .associate { it.name to (replaceArgs[it] ?: it.get(this@clone)) }

// After (O(P) with O(1) lookup):
val consParamNames = consParams.mapTo(HashSet()) { it.name }
val allValues = memberProperties
    .filter { it in mutableProperties || it.name in consParamNames }
    .associate { it.name to (replaceArgs[it] ?: it.get(this@clone)) }
```

## Speedup

~15× at P=20 properties, C=15 constructor parameters.