go-text-template 1.0.25-pr-47

text/template

This project is a C# adaptation of Go's template engine. It began as an experiment to see whether OpenAI Codex could port the Go implementation to .NET. Claude.AI helped with explanations and refinements along the way. The source code in this repository was largely produced by Codex with input from Claude.AI, and this README itself was also authored using Codex.

The original Go package can be found here:

• https://pkg.go.dev/text/template#pkg-overview
• https://cs.opensource.google/go/go/+/refs/tags/go1.24.4:src/text/template/template.go

Currently this repository demonstrates a relatively small but functional implementation. The TemplateEngine.Process helper reads templates using the ANTLR-generated GoTemplateLexer and GoTemplateParser and performs variable substitution, loops and conditionals.

Features

• Replace {{ variable }} placeholders with values from dictionaries or model objects.
• Conditional blocks with if, else if and else clauses.
• for loops and Go-style range loops over arrays, collections and maps.
• Built-in functions: eq, ne, numeric comparisons (lt, le, gt, ge), logical operators (and, or, not) supporting multiple arguments.
• Basic pipelines with the lower function for transforming output.
• Access nested properties, map keys and indexes, including dynamic indexing via variables.
• Whitespace trimming with {{- and -}} and comment syntax {{/* ... */}}.

Example Scenarios

1. Variable Interpolation

Access properties

{{ .Property }}

Nested property access

{{ .User.Name }}

Index arrays or slices

{{ .Items[0] }}

Access map entries

{{ .Data.key }}

Control whitespace

{{- .Name -}}

2. Conditional Statements

Basic if blocks

{{ if condition }}...{{ end }}

if/else blocks

{{ if condition }}...{{ else }}...{{ end }}

else if chains

{{ if condition }}...{{ else if other }}...{{ end }}

Supported conditions include

• {{ if .IsActive }}
• {{ if eq .Status "active" }}
• {{ if .User }}

3. Loop Statements

Iterate slices or arrays

{{ range .Items }}...{{ end }}

Capture index/value

{{ range $i, $v := .Items }}...{{ end }}

Iterate maps

{{ range .Map }}...{{ end }}

Map key/value variables

{{ range $k, $v := .Map }}...{{ end }}

Handle empty collections

{{ range .Items }}...{{ else }}...{{ end }}

4. Built-in Functions

Equality and inequality

eq, ne

Numeric comparisons

lt, le, gt, ge

Logical operators

and, or, not

5. Comments

Embedding comments

{{/* comment */}}

6. Pipelines

Chaining functions with |

{{ .Name | lower }}

Available pipeline helpers include

• lower - convert to lowercase
• print - concatenate values using default formatting
• printf - printf-style formatting using SprintfFormatter
• html - HTML escape the value
• js - JavaScript escape the value
• urlquery - escape for URL query parameters
• len - length of a collection or string
• index - retrieve an element by index or key
• slice - slice strings or lists
• call - invoke a function value

Registered functions can be invoked via call by name:

TemplateEngine.RegisterFunction("Add", new Func<int, int, int>((a, b) => a + b));
var result = TemplateEngine.Process("{{ call \"Add\" 1 2 }}", new {});
// result == "3"

Not Implemented Yet

• with, define, template and block directives.
• Custom functions beyond basic comparisons and boolean operators.
• Custom delimiter support.

Usage

var tmpl = "Hello {{ .Name }}!";
var result = TemplateEngine.Process(tmpl, new { Name = "World" });
Console.WriteLine(result); // Hello World!

Example Template

string letter = @"Dear {{ .Name }}
{{ if .Attended }}
It was a pleasure to see you.
{{ else }}
Sorry you couldn't make it.
{{ end }}
You brought: {{ for item in Items }}{{ item }},{{ end }}
Thank you for the lovely {{ .Gift }}.";

var output = TemplateEngine.Process(letter, new
{
    Name = "Bob",
    Gift = "toaster",
    Attended = false,
    Items = new[] { "book", "pen" }
});
Console.WriteLine(output);

See the unit tests for more examples covering loops, conditionals and range expressions.

Claude's suggestions

https://gist.github.com/yetanotherchris/c80d0fadb5a2ee5b4beb0a4384020dbf.js

License

This project is released under the MIT license. Source code was produced by OpenAI Codex with assistance from Claude.AI. This README was written using OpenAI Codex.