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What do you mean when you write that `{ "a" : "b" }` is not necessary a literal but potentially an expression?

by viebel 6y ago

dathinab 6y ago
Depending on how a language defines their syntax. Often times literals are only things like `"string"`, `0` and so one. But thinks like `[ 1,2]` would be a array expression where each "entry" is syntax wise an expression (and any literal is an expression itself). I don't know if JavaScript specifically does define object literals or object expressions, in the end it depends on what you define a literal as. Lastly depending on the language something like `[ 1,2]` might literally de-sugar to something like following pseudo code `var tmp = Array.new(capacity=2); tmp.push(1); temp.push(2)`. So a better way would be that a formulation like "data should be creatable without explicitly doing any function calls, variable assignments or similar. Creation must not depend on implicitly captured data".
- viebel 6y ago
  I totally agree with "data should be creatable without explicitly doing any function calls, variable assignments or similar." Could you explain what you mean by "Creation must not depend on implicitly captured data"?
  - dathinab 6y ago
    Lets say you have a language which has some form of macro system or similar to make creation of new thinks which look like literal-like expression easier. E.g. instead of `a = [1,2]` you have `a = vec![1,2]` which de-sugars to `a = Vec::with_capacity(2); a.push(1); a.push(2);`. Now custom data structures can define their own macros like that, e.g. `skip_list![1,2]`. Which would be all fine. But what if now `bad_skip_list![1,2]` accesses a thread local variable (or other implicit provided data) and adds that, too? Now `bad_skip_list![1,2]` might be not equal to `bad_skip_list![1,2]` defined somewhere else. Which is against the ideas behind the rule #5. You should be able to copy-past the literal-like creation of data to any place (e.g. a unit-test) and get the same result. EDIT: If I remember correctly you could override parts of `Array.prototype` and array construction in JavaScript to brake the #5 for JavaScript for thinks like `[1,2,3]` but I'm not to sure about that anymore.

What do you mean when you write that `{ "a" : "b" }` is not necessary a literal but potentially an expression?

by viebel 6y ago

What do you mean when you write that `{ "a" : "b" }` is not necessary a literal but potentially an expression?

Depending on how a language defines their syntax. Often times literals are only things like `"string"`, `0` and so one. But thinks like `[ 1,2]` would be a array expression where each "entry" is syntax wise an expression (and any literal is an expression itself). I don't know if JavaScript specifically does define object literals or object expressions, in the end it depends on what you define a literal as. Lastly depending on the language something like `[ 1,2]` might literally de-sugar to something like following pseudo code `var tmp = Array.new(capacity=2); tmp.push(1); temp.push(2)`. So a better way would be that a formulation like "data should be creatable without explicitly doing any function calls, variable assignments or similar. Creation must not depend on implicitly captured data".

viebel 6y ago
I totally agree with "data should be creatable without explicitly doing any function calls, variable assignments or similar." Could you explain what you mean by "Creation must not depend on implicitly captured data"?
- dathinab 6y ago
  Lets say you have a language which has some form of macro system or similar to make creation of new thinks which look like literal-like expression easier. E.g. instead of `a = [1,2]` you have `a = vec![1,2]` which de-sugars to `a = Vec::with_capacity(2); a.push(1); a.push(2);`. Now custom data structures can define their own macros like that, e.g. `skip_list![1,2]`. Which would be all fine. But what if now `bad_skip_list![1,2]` accesses a thread local variable (or other implicit provided data) and adds that, too? Now `bad_skip_list![1,2]` might be not equal to `bad_skip_list![1,2]` defined somewhere else. Which is against the ideas behind the rule #5. You should be able to copy-past the literal-like creation of data to any place (e.g. a unit-test) and get the same result. EDIT: If I remember correctly you could override parts of `Array.prototype` and array construction in JavaScript to brake the #5 for JavaScript for thinks like `[1,2,3]` but I'm not to sure about that anymore.