Expr does not have object identity have field equality, i.e. julia> Expr(:call, println) == Expr(:call, println) true I was surprised to learn that Expr nevertheless is mutable. I can easily imagine why Expr does not have object identity (“Oh, no, I do not mean to call this println method without …

[image] PatrickHaecker: So why is Expr mutable? One reason might be that Expr existed long before immutable structs were implemented in the language.

Why is `Expr` mutable?

stevengj Split this topic June 14, 2025, 5:42pm 10

9 posts were split to a new topic: How is Symbol special?

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Assignment and argument passing semantics Offtopic	31	2710	November 4, 2018
Mutable struct without fields behaving weirdly General Usage	14	3416	February 2, 2018
How is `Symbol` special? Internals & Design	8	182	June 14, 2025
Equality of mutable structs General Usage mutable-structure	7	549	December 5, 2023
Expressions with Arbitrary Objects in their `args` Arguments Internals & Design question , macros , metaprogramming	6	507	April 8, 2023