---
title: "How Ruby Implements Closures: What Really Happens When You Call lambda"
url: https://daily.dev/posts/how-ruby-implements-closures-what-really-happens-when-you-call-lambda-iuict0hih
source_url: https://rubystacknews.com/2026/06/24/how-ruby-implements-closures-what-really-happens-when-you-call-lambda
type: article
source: "Ruby Flow"
published: 2026-06-25T08:12:08.390Z
updated: 2026-06-25T08:12:29.195Z
tags: ["ruby"]
reading_time: 4
upvotes: 0
comments: 0
language: en
---

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# How Ruby Implements Closures: What Really Happens When You Call lambda

**[Ruby Flow](https://daily.dev/sources/rubyflow)** · 4 min read · 0 upvotes · 0 comments

## Summary

A deep dive into how Ruby's YARV virtual machine implements closures under the hood. When a lambda or proc captures a local variable, Ruby copies the current stack frame environment to the heap, creating an rb_env_t object. Crucially, Ruby then redirects the Environment Pointer (EP) to the heap copy, so all subsequent variable accesses — including mutations — go through the heap. This explains why multiple lambdas in the same scope share the same captured variables (they reuse the same rb_env_t), why variable modifications after lambda creation are visible inside the closure, and why local variables survive after their enclosing method returns. Internally, both lambda and Proc.new produce an rb_proc_t object distinguished only by an is_lambda boolean flag.

## Full article

daily.dev links to this article rather than hosting it. Read it at the original source: <https://rubystacknews.com/2026/06/24/how-ruby-implements-closures-what-really-happens-when-you-call-lambda>

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