Table of Contents

Getting Started

Installation

Install the core package from NuGet:

dotnet add package Invex.Rez

If you want to resolve templates inside Microsoft.Extensions.Configuration values, also install the configuration package:

dotnet add package Invex.Rez.Configuration

Both packages target net10.0, net9.0, net8.0, and netstandard2.0, so they can be used from modern .NET, .NET Framework, and anything else that supports .NET Standard 2.0.

Your first template

Resolving a template takes three steps:

  1. Instantiate an implementation of IResolver (e.g., Resolver).
  2. Add one or more sources of variables and functions (IResolverSource implementations).
  3. Call Resolve(), passing in the text to be resolved.
using Invex.Rez.Abstraction;
using Invex.Rez.Implementation;

var resolver = new Resolver();

resolver.AddSource(new ResolverSource(new Dictionary<string, string>
{
    { "name", "World" }
}));

var greeting = resolver.Resolve("Hello, {name}!");

// greeting: "Hello, World!"

Adding functions

Functions are written in templates as {name(args)}. A function is a Func<FunctionCall, string> — it receives the raw argument text via FunctionCall.Args and returns the result:

var resolver = new Resolver();

resolver.AddSource(new ResolverSource(new Dictionary<string, Func<FunctionCall, string>>
{
    { "shout", call => (call.Args ?? string.Empty).ToUpperInvariant() + "!!!" }
}));

var output = resolver.Resolve("{shout(hello)}");

// output: "HELLO!!!"
Note

The argument text between the parentheses is passed to the function as a single string. The function itself is responsible for any parsing (e.g., splitting on commas) — no splitting or trimming is performed by Rez.

Mutable sources with ResolverStore

ResolverSource is immutable — its contents are fixed at construction time. When you need to add and remove variables or functions at runtime, use ResolverStore:

var store = new ResolverStore();
var resolver = new Resolver().AddSource(store);

store.AddVariable("user", "Alice");
store.AddFunction("now", _ => DateTime.UtcNow.ToString("O"));

var line = resolver.Resolve("[{now()}] {user} logged in");

store.RemoveVariable("user");

Adding a variable or function with a name that already exists replaces the existing entry.

Multiple sources and ordering

A resolver can have any number of sources. When resolving a placeholder, sources are queried in the order they were added, and the first non-null result wins:

var overrides = new ResolverStore();
var defaults  = new ResolverSource(new Dictionary<string, string>
{
    { "env", "production" }
});

var resolver = new Resolver()
    .AddSource(overrides)   // queried first
    .AddSource(defaults);   // queried second

resolver.Resolve("{env}");  // "production"

overrides.AddVariable("env", "development");

resolver.Resolve("{env}");  // "development" — the override wins

This makes it easy to layer sources: put overrides first and fallbacks last.

What happens when something can't be resolved?

Placeholders that no source can resolve are left in the output unchanged:

resolver.Resolve("Hello, {unknown}!");

// "Hello, {unknown}!"

This means a missing variable never throws — the template degrades gracefully.

Next steps

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