generic_api_demo

Generic ClassAd API Demo

This example demonstrates the new idiomatic generic API for working with ClassAds: Set(), GetAs[T](), and GetOr[T]().

Overview

The generic API provides a more Go-idiomatic way to work with ClassAds, reducing verbosity and leveraging Go's type inference and generics.

Features

1. Generic Set() Method

Set any type of value without type-specific methods:

ad := classad.New()
ad.Set("cpus", 4)              // int
ad.Set("price", 0.05)          // float64
ad.Set("name", "worker-1")     // string
ad.Set("enabled", true)        // bool
ad.Set("tags", []string{"a"})  // slice
ad.Set("config", nestedAd)     // *ClassAd
ad.Set("formula", expr)        // *Expr

Old API:

ad.InsertAttr("cpus", 4)
ad.InsertAttrFloat("price", 0.05)
ad.InsertAttrString("name", "worker-1")
ad.InsertAttrBool("enabled", true)

2. Type-Safe GetAs[T]() Method

Retrieve values with compile-time type safety:

cpus, ok := classad.GetAs[int](ad, "cpus")
name, ok := classad.GetAs[string](ad, "name")
tags, ok := classad.GetAs[[]string](ad, "tags")
config, ok := classad.GetAs[*classad.ClassAd](ad, "config")

Old API:

cpus, ok := ad.EvaluateAttrInt("cpus")
name, ok := ad.EvaluateAttrString("name")
// Slices required more complex handling

3. Convenient GetOr[T]() with Defaults

Eliminate boilerplate if-checks by providing defaults:

cpus := classad.GetOr(ad, "cpus", 1)           // Defaults to 1
timeout := classad.GetOr(ad, "timeout", 300)   // Defaults to 300
owner := classad.GetOr(ad, "owner", "unknown") // Defaults to "unknown"

Old API:

var cpus int64
if val, ok := ad.EvaluateAttrInt("cpus"); ok {
    cpus = val
} else {
    cpus = 1
}

Running the Example

go run main.go

Examples in This Demo

1. Basic Set and Get: Simple type handling
2. GetOr with Defaults: Eliminating nil checks
3. Working with Slices: Arrays of values
4. Nested ClassAds: Complex hierarchical data
5. Expressions: Unevaluated formulas
6. Type Conversion: Automatic int/float conversions
7. API Comparison: Old vs new approaches
8. Real-World Config: Practical configuration example

Benefits

Less Verbose

• Set("x", 5) vs InsertAttr("x", 5)
• No need to remember method names for each type

Type Inference

• Compiler infers types automatically
• Fewer type annotations needed

Defaults Made Easy

• GetOr(ad, "timeout", 300) handles missing values
• Eliminates if-checks and nil handling

Type Safety

• Compile-time type checking with generics
• GetAs[int]() ensures you get an int

Consistent API

• Same pattern for all types
• Easier to learn and remember

Backward Compatibility

The old API remains available:

• InsertAttr(), InsertAttrString(), etc. still work
• EvaluateAttrInt(), EvaluateAttrString(), etc. still work
• Existing code continues to function

The generic API is additive and provides an alternative, more idiomatic approach.

Type Support

Supported types:

• Integers: int, int8, int16, int32, int64, uint, uint8, etc.
• Floats: float32, float64
• Strings: string
• Booleans: bool
• Slices: []T for any supported type T
• ClassAds: *classad.ClassAd
• Expressions: *classad.Expr
• Structs: Any struct (marshaled to nested ClassAd)

Automatic Type Conversion

The API handles common conversions:

ad.Set("value", 42)

// All of these work:
asInt, _ := classad.GetAs[int](ad, "value")       // 42
asInt64, _ := classad.GetAs[int64](ad, "value")   // 42
asFloat, _ := classad.GetAs[float64](ad, "value") // 42.0

Use Cases

Configuration Files

serverName := classad.GetOr(config, "server_name", "default")
port := classad.GetOr(config, "port", 8080)
timeout := classad.GetOr(config, "timeout", 30)

Job Specifications

ad.Set("RequestCpus", 4)
ad.Set("RequestMemory", 8192)
ad.Set("Owner", "alice")

cpus := classad.GetOr(ad, "RequestCpus", 1)
memory := classad.GetOr(ad, "RequestMemory", 1024)

Dynamic Templates

formula, _ := classad.ParseExpr("RequestCpus * 2")
ad.Set("ComputedCpus", formula)

expr, _ := classad.GetAs[*classad.Expr](ad, "ComputedCpus")
result := expr.Eval(ad)

See Also

• MARSHALING.md - Struct marshaling guide
• struct_demo - Struct marshaling examples
• api_demo - Original API examples