---
title: 'ARC0028: Move inline generation to a generated parameter'
editUrl: https://github.com/Cratis/Arc/edit/main/Documentation/backend/csharp/code-analysis/ARC0028.md
description: Make inline concept generation pinnable by moving it to a generated Handle parameter.
---


## Rule

Inside a model-bound command's instance `Handle()`, Arc recognizes a concept's `X.New()`
or a `GenerateValue.*(...)` / `Guid.NewGuid()` result directly converted or wrapped into a
self-generatable concept. **Default severity: Info.** Raw primitives, helpers outside Handle,
and generation inside nested functions are not reported.

## Diagnostic example

The examples use this identifier, the same declaration as in
[generated values](/arc/backend/csharp/commands/generated-values/):

```csharp
using System;
using Cratis.Arc.Commands.ModelBound;
using Cratis.Concepts;

public record CartId(Guid Value) : ConceptAs<Guid>(Value), IGeneratable<CartId>
{
    public static CartId New() => new(GenerateValue.Uuid());
}
```

Compile this command together with it:

```csharp
[Command]
public record AllocateCartId
{
    public CartId Handle() => CartId.New();
}
```

## Quick fix

**Move to a [GeneratedValue] parameter** adds a concept-typed parameter and replaces the
whole generation expression with its name:

```csharp
[Command]
public record AllocateCartId
{
    public CartId Handle([GeneratedValue] CartId cartId) => cartId;
}
```

The fix derives a name from the local variable, argument, or concept and avoids existing
names. It keeps required parameters before optional or `params` parameters. Choose an explicit
attribute name afterward if scenario pins should survive a C# parameter rename.

The fix is deliberately local; it does not update direct Handle callers or move generation
inside loops, branches, nested functions, virtual/override methods, or interface implementations. Nonconstant strategy
arguments also prevent the fix. These cases need a manual migration so you can preserve
allocation timing and cardinality. No Fix All action is offered.

Review the concept's factory before accepting: the parameter uses that factory, not arbitrary
strategy arguments from the old expression. Follow [migrating generated identifiers](/arc/upgrading/generated-values/)
for scenario pins and context-dependent strategies.