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13515c5eb0
This adds support for (limited) mutable variables. Mutable variables are created with mut much the same way immutable variables are made with let.
Mutable variables allow mutation via the assignment operator (=).
❯ mut x = 100
❯ $x = 200
❯ print $x
200
Mutable variables are limited in that they're only tended to be used in the local code block. Trying to capture a local variable will result in an error:
❯ mut x = 123; {|| $x }
Error: nu::parser::expected_keyword (link)
× Capture of mutable variable.
The intent of this limitation is to reduce some of the issues with mutable variables in general: namely they make code that's harder to reason about. By reducing the scope that a mutable variable can be used it, we can help create local reasoning about them.
Mutation can occur with fields as well, as in this case:
❯ mut y = {abc: 123}
❯ $y.abc = 456
❯ $y
On a historical note: mutable variables are something that we resisted for quite a long time, leaning as much as we could on the functional style of pipelines and dataflow. That said, we've watched folks struggle to work with reduce as an approximation for patterns that would be trivial to express with local mutation. With that in mind, we're leaning towards the happy path.
67 lines
1.2 KiB
Rust
67 lines
1.2 KiB
Rust
mod alias;
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mod ast;
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mod commandline;
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mod debug;
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mod def;
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mod def_env;
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mod describe;
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mod do_;
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mod echo;
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mod error_make;
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mod export;
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mod export_alias;
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mod export_def;
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mod export_def_env;
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mod export_extern;
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mod export_use;
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mod extern_;
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mod for_;
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pub mod help;
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mod hide;
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mod hide_env;
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mod if_;
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mod ignore;
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mod let_;
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mod metadata;
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mod module;
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mod mut_;
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pub(crate) mod overlay;
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mod use_;
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mod version;
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pub use alias::Alias;
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pub use ast::Ast;
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pub use commandline::Commandline;
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pub use debug::Debug;
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pub use def::Def;
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pub use def_env::DefEnv;
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pub use describe::Describe;
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pub use do_::Do;
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pub use echo::Echo;
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pub use error_make::ErrorMake;
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pub use export::ExportCommand;
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pub use export_alias::ExportAlias;
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pub use export_def::ExportDef;
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pub use export_def_env::ExportDefEnv;
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pub use export_extern::ExportExtern;
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pub use export_use::ExportUse;
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pub use extern_::Extern;
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pub use for_::For;
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pub use help::Help;
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pub use hide::Hide;
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pub use hide_env::HideEnv;
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pub use if_::If;
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pub use ignore::Ignore;
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pub use let_::Let;
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pub use metadata::Metadata;
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pub use module::Module;
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pub use mut_::Mut;
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pub use overlay::*;
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pub use use_::Use;
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pub use version::Version;
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#[cfg(feature = "plugin")]
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mod register;
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#[cfg(feature = "plugin")]
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pub use register::Register;
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