feat: describe evaluation strategies of Tact #311
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| ### Binding strategy [#runtime-binding] | ||
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| Tact uses the [call by value (CBV)](https://en.wikipedia.org/wiki/Evaluation_strategy#Call_by_value) parameter-passing and binding strategy. That is, the evaluated value of any variable passed in a function call (except for [receivers](/book/contracts#receiver-functions) and [getters](/book/contracts#getter-functions)) or assigned in the [`let{:tact}`](/book/statements#let) or [assignment](/book/statements#assignment) statement is copied. This prevents mutations of the original values in different scopes, but increases the gas usage. |
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Let's also clarify that copying happens for structs and maps as well
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The draft looks good! |
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| ### Binding strategy [#runtime-binding] | ||
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| Tact uses the [call by value (CBV)](https://en.wikipedia.org/wiki/Evaluation_strategy#Call_by_value) parameter-passing and binding strategy. That is, the evaluated value of any variable passed in a function call (except for [receivers](/book/contracts#receiver-functions) and [getters](/book/contracts#getter-functions)) or assigned in the [`let{:tact}`](/book/statements#let) or [assignment](/book/statements#assignment) statement is copied. This prevents mutations of the original values in different scopes, but increases the gas usage. |
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There is one missing piece though: mutating methods! Those cannot not copy their self argument
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Yes, but those aren't part of the binding strategy, just as assignments to struct/message fields, map.set()/del(), or any other re-assignments to local or state/storage variables. Like, the only things actively preventing re-assignments are constants :)
I can create a list of "allowed mutations" or say something about constants, not sure
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what about things like "small byte arrays"? tact-lang/tact#163 (comment)
WIP: Need to move/refine examples of assignments and function calls from the playground contracts
Closes #251
Towards #105 (in some sense)