# A bare scope block (\`do:\`) — worth adding?

**URL:** <https://forum.modular.com/t/a-bare-scope-block-do-worth-adding/3661>\
**Category:** Mojo\
**Created:** [November 11, 2026, 9:04pm UTC](https://forum.modular.com/t/a-bare-scope-block-do-worth-adding/3661 "2026-11-11T21:04:50Z")\
**Posts on this page:** 4\
**Page:** 1

<div class="post-metadata">

**Author:** ![muz](https://avatars.discourse-cdn.com/v4/letter/m/bc8723/32.png) [@muz](https://forum.modular.com/u/muz)\
**Post date:** [November 11, 2026, 9:04pm UTC](https://forum.modular.com/t/a-bare-scope-block-do-worth-adding/3661/1 "2026-11-11T21:04:50Z")

</div>

Hi all,

In Mojo there’s no way to introduce a _standalone_ scope - something like C’s bare `{ ... }`. I keep wanting this for two common cases:

1. **Limiting the visibility of temporaries.** In a long function I often compute a bunch of intermediate values (e.g. series coefficients) that are only needed for a few lines. A scope keeps them from leaking into the rest of the function and prevents accidental reuse.
2. **Controlling destruction timing.** A scope forces `var`s to be destroyed at a well-defined point rather than at end of function.

The current workarounds all have problems:

- **`if True:`** - works, but the compiler recognizes the constant condition and emits an “unreachable code” warning. The warning is correct behavior for real code, which makes it a poor idiom for intentional scoping.
- **`try: ... finally: pass`** - compiles and creates a scope, but it’s semantically misleading: readers will reasonably assume error handling is involved. Using an error-handling construct purely for scoping obscures intent.
- **Nested `def`** - creates a scope but adds call machinery and capture semantics; overkill.

So: would a bare block statement be a good addition? Something like:

```mojo
var x = compute_header()  
do: 
    var tmp1 = expensive_intermediate()  
    var tmp2 = another_intermediate(tmp1)  
    x = combine(x, tmp2)  

# tmp1, tmp2 no longer visible here

```

Thanks!

---

<div class="post-metadata">

**Author:** ![owenhilyard](https://sea1.discourse-cdn.com/flex001/user_avatar/forum.modular.com/owenhilyard/32/41_2.png) [@owenhilyard](https://forum.modular.com/u/owenhilyard)\
**Post date:** [November 11, 2026, 9:24pm UTC](https://forum.modular.com/t/a-bare-scope-block-do-worth-adding/3661/2 "2026-11-11T21:24:25Z")

</div>

> **Controlling destruction timing.** A scope forces `var`s to be destroyed at a well-defined point rather than at end of function.

Mojo has ASAP destruction, so values are destroyed after their last use.

I don’t really have opinions on adding scopes like this so I’ll leave that be.

---

<div class="post-metadata">

**Author:** ![muz](https://avatars.discourse-cdn.com/v4/letter/m/bc8723/32.png) [@muz](https://forum.modular.com/u/muz)\
**Post date:** [November 11, 2026, 9:54pm UTC](https://forum.modular.com/t/a-bare-scope-block-do-worth-adding/3661/3 "2026-11-11T21:54:42Z")

</div>

Ah, you’re right @owenhilyard - thanks for the correction. Old habits die hard; I was still thinking in terms of scope-bound RAII…

---

<div class="post-metadata">

**Author:** ![juliawhite](https://avatars.discourse-cdn.com/v4/letter/j/50afbb/32.png) [@juliawhite](https://forum.modular.com/u/juliawhite)\
**Post date:** [November 12, 2026, 3:24am UTC](https://forum.modular.com/t/a-bare-scope-block-do-worth-adding/3661/4 "2026-11-12T03:24:40Z")

</div>

With ASAP destruction covering the timing argument, the remaining case is name hygiene alone—which still has precedent: Rust’s bare `{ }` blocks and Swift’s `do { }` exist exactly for that, and readers recognize the idiom. Whether it earns new syntax is a judgement call, but it might be worth first asking whether the `if True:` unreachable warning could be suppressed (or a sanctioned scoping idiom documented), since that would capture most of the benefit without adding surface area.