The Three Match Kinds¶

MonoWeaver splits targets into three kinds. Picking the wrong kind is the number one reason nothing matches, so decide this first.

Target	When to use it	Examples
`Cil.Value(...)`	The code produces a value	damage calculation, field read, method return value
`Cil.Effect(...)`	The code only performs an action and leaves nothing behind	playing a sound, raising an event, calling a `void` method
`Cil.Condition(...)`	The code decides which branch is taken	`if`, `while`, `&&`, `\\|\\|`

Value¶

var damagePattern = Cil.Value((int baseDamage, int bonus) =>
    baseDamage + bonus);

A value match points at one occurrence where that value is produced. It can be read, replaced, or surrounded with new code.

Effect¶

var soundPattern = Cil.Effect((int soundId) =>
    GameAudio.Play(soundId));

An effect match covers a complete piece of code that produces no result. If the target method does return a value but the call site discards it, still use Cil.Effect(...); in the CilExpr form that is Cil.Discard(expression).

Condition¶

var gatePattern = Cil.Condition((bool left, bool right) =>
    left && right);

A condition match finds the test that decides control flow, including the short-circuit structure of && and ||. It is not searching for an ordinary bool value.

A condition is not a bool value

In return a && b; the a && b is a value. In if (a && b) it is a condition. Same source, different IL shape.

Which operations each kind supports¶

	`Before`	`After`	`Transform`	`Observe`	`Replace`	`Remove`
Value	✓	✓	✓	✓	✓	—
Effect	✓	✓	—	—	✓	✓
Condition	✓	—	✓	✓	✓	—

The two gaps have reasons:

An effect has no Transform/Observe: there is no value to read or replace.
A condition has no After: a condition can finish at different places (a short circuit jumps away early), so there is no single "line after it".

Some very complex conditions can be recognised but not safely rewritten. Check first:

if (!condition.CanRewrite)
    Console.WriteLine(condition.RewriteFailureReason);

Per-operation semantics: Rewrite Operations.