Converting To Strong Types

Converting to Strong Types

Replaces loose object and array parameter types with strong alternatives for compile-time validation and autocompletion.

Conversion Workflow

Copy and track progress:

Conversion Progress:
- [ ] Step 1: Identify loose types
- [ ] Step 2: Analyze parameter usage
- [ ] Step 3: Choose conversion strategy
- [ ] Step 4: Define types and update parameters
- [ ] Step 5: Validate with bicep build

Step 1: Identify loose types

Search for param <name> object and param <name> array declarations.

Step 2: Analyze parameter usage

Examine how the parameter is used in the template to determine expected structure.

Step 3: Choose conversion strategy

Step 4: Define types and update parameters

Place type definitions above parameters. Add @description() decorators.

Step 5: Validate

Run bicep build <file> to verify syntax and type correctness.

Quick Reference

Simple Arrays

// Before
param addresses array

// After
param addresses string[]

Union Types (Constrained Values)

param environments ('dev' | 'staging' | 'prod')[]
param skuName 'Standard_LRS' | 'Premium_LRS'

User-Defined Types

type subnetType = {
  name: string
  addressPrefix: string
  nsgId: string?  // Optional property
}

param subnets subnetType[]

Resource-Derived Types

// Derive from Azure schema (Bicep 0.34.1+)
type accountKind = resourceInput<'Microsoft.Storage/storageAccounts@2024-01-01'>.kind
param storageProps resourceInput<'Microsoft.Storage/storageAccounts@2024-01-01'>.properties

For full resource-derived type details: See RESOURCE-DERIVED.md

Type Best Practices

• Use ? for optional properties: description: string?
• Use @sealed() to prevent extra properties at deployment
• Use @description() on types and properties
• Use constraints: @minLength(), @maxLength(), @minValue(), @maxValue()
• Compose complex types from simpler types

Common Patterns

For ready-to-use type definitions: See PATTERNS.md

Includes: tags, access policies, subnets, diagnostic settings, role assignments, private endpoints.

MCP Tools

Edge Cases

Dynamic objects (unknown keys): Use wildcard { *: string }

Mixed-type arrays: Use union (string | int | bool)[]

Backward compatibility: Use optional types ? for new properties