V for C#/Java developers — Mission

Version studied

V 0.5.2, the release of July 2026. Every example of this course is in code/v-for-csharp-java, next to its expected output. .github/workflows/v-examples.yml installs V 0.5.2 from the GitHub release on Linux, Windows and macOS, runs every example, compiles every snippet a lesson shows as rejected, and compares the outputs and compiler messages with the ones pasted in the lessons.

Why I’m learning this

V promises a small language, close to Go, that compiles to C in about a second, with immutable variables by default, no null, no exceptions, and a garbage collector you can turn off. I write C# and read plenty of Java. I want to know which of these promises hold in version 0.5.2, what V costs in exchange, and where its documentation and its compiler disagree.

Who this course is for

You are comfortable with C# or Java: classes, interfaces, generics, exceptions, collections, LINQ or streams. You have never written V, and you don’t need to know C. Each lesson starts from the concept you already know and shows where V agrees, where it differs, and what the compiler says when you get it wrong.

V in one table

	C#	Java	V
Compiles to	IL, run by the CLR	bytecode, run by the JVM	C, compiled to a native executable
Build tool	dotnet	Maven, Gradle	v itself
Project file	.csproj	pom.xml, build.gradle	v.mod (optional)
Local variable	var x = 1; (mutable)	var x = 1; (mutable)	x := 1 (immutable), mut x := 1
Class	class, record, struct	class, record	struct with methods, no inheritance
Absent value	null, int?	null, Optional<T>	?T and none
Failure	exceptions	checked and unchecked exceptions	!T, error() and or { }
Memory	generational GC	GC (G1 by default)	Boehm GC by default, -autofree, -gc none
Namespaces	namespace	package	one module per folder
Visibility	public, internal, private	public, package-private, private	pub or private to the module

Sources: .NET garbage collection, G1 garbage collector, V documentation.

The documentation and the version

docs.vlang.io is built from doc/docs.md on V’s master branch, which has moved on since 0.5.2: its page The default compiler, for example, isn’t in the documentation of 0.5.2. This course links to docs.vlang.io for the concepts and checks every behavior with 0.5.2 itself; the documentation of the version studied is doc/docs.md at the 0.5.2 tag, and the standard library is described at modules.vlang.io.

The data

Lessons 3 and 4 read code/v-for-csharp-java/data/pages.csv: the 319 pages of this site at commit cbcbb42, with their locale, course, title and number of lines. It is a copy of the file the LadybugDB course extracts from this repository.

Lessons 5 to 8 read code/v-for-csharp-java/data/ga: the 111 .NET projects of GuitarAlchemist/ga at commit a26a7893, their 266 project references and 478 package references, copied from the LadybugDB course too. Lesson 7 walks their references in parallel, lesson 8 tests a module that parses them.

By the end of this course, I will be able to

• install V on Windows, Linux and macOS, and organize a program in modules;
• model data with structs, methods, interfaces and sum types instead of classes;
• handle absence and failure with ?, ! and or { } instead of null and exceptions;
• say where an array, a map or a struct is copied, shared or freed;
• write concurrent code with spawn and channels;
• test, format and document a module, and call a C library.

Outline

#	Lesson	You already know
1	Installation, v run, modules and projects	dotnet new, dotnet run, javac, java
2	Types, immutable variables, structs and methods	var, readonly/final, classes, records
3	Errors: ?, ! and or { }	null, Optional, exceptions
4	Arrays, maps, slices and memory	List<T>, Dictionary, ArrayList, HashMap, the GC
5	Interfaces and generics	interfaces, generics, constraints
6	Enums, sum types and match	enums, sealed hierarchies, switch expressions
7	Concurrency: spawn, channels and shared	Task, CompletableFuture, virtual threads, lock/synchronized
8	Tests, v fmt, v vet and v doc	xUnit/JUnit, dotnet format, analyzers, XML doc comments
9	Calling C (coming next)	P/Invoke, JNI, the FFM API
10	JSON and a web server with veb	System.Text.Json, ASP.NET Core, Jackson, Spring
11	The ORM and SQLite	Entity Framework, JPA
12	Packages, cross-compilation and deployment	NuGet/Maven Central, dotnet publish, jlink
—	Journal

Resources

• V documentation, and doc/docs.md at the 0.5.2 tag
• V standard library
• V source code, and the 0.5.2 release this course uses
• V’s language tests: the documentation says the compiler and its tests are the reference when they disagree with it