tern — Ternary & Conditional Helpers for Go

tern is a small generic utility library for Go that brings ternary-like expressions and a variety of conditional helpers to make complex branching more concise, readable, and type-safe.

It supports lazy evaluation, chainable if/else-if/else flows, value/predicate-based switch/case, nullish coalescing for zero-values and pointers, and error-aware selectors.

Module: github.com/aminofox/tern
Go version: 1.20+ (1.22 recommended)

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Installation

go get github.com/aminofox/tern

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Features

• Ternary Expressions

  • T(cond, thenVal, elseVal) — eager
  • TF(cond, thenFn, elseFn) — lazy (evaluates only the selected branch)

• Chainable Conditions (fluent, lazy)

  • When/WhenFn → ElseIf/ElseIfFn → Else/ElseFn

• Switch/Case Style Matching

  • Match by value: .Case(val, result), .CaseFn(val, func() R)
  • Match by predicate: .CaseWhen(pred, result), .CaseWhenFn(pred, func() R)
  • Fallback: .Default(def), .DefaultFn(func() R)

• Nullish / Coalesce Helpers

  • FirstNonZero(vals...) — first non-zero-value element
  • OrElse, OrElseFn — zero-value fallback (lazy and eager versions)
  • PtrOr, PtrOrFn — pointer fallback (lazy and eager)
  • PtrCoalesce(vals...) — first non-nil pointer

• Error-Aware Helpers

  • IfErr(val, err, fallback) — fallback on error
  • IfErrFn(val, err, func(error) T) — lazy fallback on error
  • Choose(producers...) — runs multiple producers until one returns (val, true)

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Quick Examples

import (
    "fmt"
    "strings"

    "github.com/aminofox/tern"
)

// Ternary with nested conditions (lazy)
res := tern.TF[string](
    len(items) > 0,
    func() string { return strings.Join(items, ", ") },
    func() string {
        s := strings.TrimSpace(maybe)
        return tern.T[string](s != "", s, "N/A")
    },
)
fmt.Println(res) // "apple, banana"

// Chain if/else-if/else
grade := tern.When[string](score >= 90, "A").
    ElseIf(score >= 80, "B").
    ElseIf(score >= 70, "C").
    Else("D")

// Switch/case with predicate
perm := tern.Match[string, int](role).
    Case("root", 4).
    Case("admin", 3).
    CaseWhen(func(r string) bool { return strings.HasPrefix(r, "mod") }, 2).
    Default(1)

// Nullish coalescing
name := tern.PtrOr(user.Nickname, "Guest")
limit := tern.OrElse(req.Limit, 50)
first, _ := tern.FirstNonZero("", "abc", "xyz")

// Error-aware fallback
data, err := service.Load()
out := tern.IfErrFn(data, err, func(e error) string { return "cached" })

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Running Tests & Examples

Run the full test suite (includes Example... functions that also appear in GoDoc):

go test ./...

Run the CLI example:

go run ./examples

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Design Notes

• All functions with the Fn suffix are lazy — only the selected branch is evaluated.
• FirstNonZero works based on the Go zero-value for the type.
• Match short-circuits on the first matching case.
• Fully generic and type-safe (requires Go 1.18+).

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License

MIT