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Nevertheless, scope wise it behaves like an implicit parameter with lexical scope. It just muddies the issue to talk about dynamic scope.

by goto11 7y ago

DonHopkins 7y ago
Dude or dudess, "this" absolutely does not behave in any way like it is lexically scoped, in any sense of the term. Reality check: Are we even talking about the same language? I'm talking about JavaScript. Which language are you talking about, C++? If you're not talking about JavaScript, then you replied to the wrong comment. Or are you just trolling and gaslighting, because you were offended by the Trump reference? I'll give you the benefit of the doubt that you're also referring to JavaScript, and that you sincerely believe what you say, because you need to change your beliefs. Please go read any elementary JavaScript tutorial, or any of the thousands of blog posts by people who got screwed by accidentally mis-understanding for a moment and mistakenly thinking that "this" was lexically scoped, then got burnt, but learned from the experience, and wanted to share with everyone else what they learned by shooting themselves with an "oft-fired footgun": "this" is dynamically scoped, and changes meaning at runtime, regardless of the surrounding lexical environment in which it was defined, UNLESS you use fat arrow functions, which were specifically designed to work around that problem. If "this" behaved like an implicit parameter with lexical scope, then why did they bother adding fat arrow functions to the language as an afterthought, to work around the problem you don't seem to believe exists? One more time, I will quote the rationale section of Brendan Eich's fat arrow proposal: https://tc39wiki.calculist.org/es6/arrow-functions/ https://tc39wiki.calculist.org/es6/arrow-functions/ >"dynamic this binding is an oft-fired footgun" -Brendan Eich, ES6 Arrow Functions Proposal If you're right, then Brendan Eich, Douglas Crockford, Anders Hejlsberg, many other expert designers and programmers of JavaScript and TypeScript, and a whole lot of other people, are also extremely confused: https://www.forumone.com/ideas/typescript-application-scale-javascript/ https://www.forumone.com/ideas/typescript-application-scale-... >TypeScript borrows some features from the upcoming ECMAScript 6 specification, too. There is convenience syntax for day-to-day programming tasks, such as the arrow function, borrowed from CoffeeScript. The arrow function, which looks like this: (foo, bar) => baz, is shorthand notation for (function (foo, bar) { return baz; }).bind(this). This automatically captures the current value of “this” in scope, which is more often than not what you want. The proposal even states “dynamic this binding is an oft-fired footgun.” http://jsnext.blogspot.com/2012/07/arrow-functions.html http://jsnext.blogspot.com/2012/07/arrow-functions.html >Arrow Functions are lexically bound to the 'this' of where it is declared. In other words, when an Arrow Function is declared, whatever the scope is at that time, that is 'this'. [...] Why add Arrow Functions? Why add this? We already understood what was going on... so why change it? I think that Brendan Eich has provided a great list of reasons ('Rationale' section): [...] However, we don’t want CoffeeScript’s ->, it’s confusing to have two arrows and dynamic this binding is an oft-fired footgun. What exactly do you believe Brendan Eich meant by "dynamic this binding"? How can "this" be dynamically bound, yet behave "like an implicit parameter with lexical scope" (as you wrongly claim) at the same time? Is Brendan Eich and everyone else in the JavaScript and TypeScript communities mistaken, and they foolishly added fat arrow functions to JavaScript for no reason, but nobody pointed out that embarrassing mistake until you came along? If you're right, then you're barking up the wrong tree by arguing with me about it, so by all means, get on Twitter and tell Brendan Eich himself, ASAP! Your argument is with him and everyone else, not me. Maybe it's not too late to turn that ship around, but in my opinion it's already sailed. But if you're wrong, then you probably have a lot of bugs to fix in your code, and should stay off Twitter. If you truly believe in your heart of hearts that "this" is lexically scoped, you have definitely proven my and Brendan's point that "this" is a terrible "oft-fired footgun" that causes lots of deep confusion and insidious misunderstanding: just take a step back and look at how sure you are of yourself. Because "this" is certainly more mysterious and dangerous than YOU believe it is.
- goto11 7y ago
  Regular JavaScript functions work as if there is an implicit "this" parameter (which gets the value from the left-hand side of the call expression rather than the argument list). Fat-arrow function on the other hand does not change "this", which means the "this" binding inside a fat-arrow function is the one from the containing scope. But in both cases the scope of the "this" binding is lexical. Dynamic scope means something different. Dynamic scope means that a variable binding from the call site is visible in a called function and down the call stack. This is not how "this" works. The "this" binding at the call site is never visible inside the called function, unless the called function happen to be nested inside the same lexical scope. "this" is confusing because it gets rebound at every call, even if the function is not called using dot expression. But it is not because of dynamic scoping.

Nevertheless, scope wise it behaves like an implicit parameter with lexical scope. It just muddies the issue to talk about dynamic scope.

by goto11 7y ago

Nevertheless, scope wise it behaves like an implicit parameter with lexical scope. It just muddies the issue to talk about dynamic scope.

DonHopkins 7y ago

Dude or dudess, "this" absolutely does not behave in any way like it is lexically scoped, in any sense of the term. Reality check: Are we even talking about the same language? I'm talking about JavaScript. Which language are you talking about, C++? If you're not talking about JavaScript, then you replied to the wrong comment. Or are you just trolling and gaslighting, because you were offended by the Trump reference? I'll give you the benefit of the doubt that you're also referring to JavaScript, and that you sincerely believe what you say, because you need to change your beliefs. Please go read any elementary JavaScript tutorial, or any of the thousands of blog posts by people who got screwed by accidentally mis-understanding for a moment and mistakenly thinking that "this" was lexically scoped, then got burnt, but learned from the experience, and wanted to share with everyone else what they learned by shooting themselves with an "oft-fired footgun": "this" is dynamically scoped, and changes meaning at runtime, regardless of the surrounding lexical environment in which it was defined, UNLESS you use fat arrow functions, which were specifically designed to work around that problem. If "this" behaved like an implicit parameter with lexical scope, then why did they bother adding fat arrow functions to the language as an afterthought, to work around the problem you don't seem to believe exists? One more time, I will quote the rationale section of Brendan Eich's fat arrow proposal: https://tc39wiki.calculist.org/es6/arrow-functions/ https://tc39wiki.calculist.org/es6/arrow-functions/ >"dynamic this binding is an oft-fired footgun" -Brendan Eich, ES6 Arrow Functions Proposal If you're right, then Brendan Eich, Douglas Crockford, Anders Hejlsberg, many other expert designers and programmers of JavaScript and TypeScript, and a whole lot of other people, are also extremely confused: https://www.forumone.com/ideas/typescript-application-scale-javascript/ https://www.forumone.com/ideas/typescript-application-scale-... >TypeScript borrows some features from the upcoming ECMAScript 6 specification, too. There is convenience syntax for day-to-day programming tasks, such as the arrow function, borrowed from CoffeeScript. The arrow function, which looks like this: (foo, bar) => baz, is shorthand notation for (function (foo, bar) { return baz; }).bind(this). This automatically captures the current value of “this” in scope, which is more often than not what you want. The proposal even states “dynamic this binding is an oft-fired footgun.” http://jsnext.blogspot.com/2012/07/arrow-functions.html http://jsnext.blogspot.com/2012/07/arrow-functions.html >Arrow Functions are lexically bound to the 'this' of where it is declared. In other words, when an Arrow Function is declared, whatever the scope is at that time, that is 'this'. [...] Why add Arrow Functions? Why add this? We already understood what was going on... so why change it? I think that Brendan Eich has provided a great list of reasons ('Rationale' section): [...] However, we don’t want CoffeeScript’s ->, it’s confusing to have two arrows and dynamic this binding is an oft-fired footgun. What exactly do you believe Brendan Eich meant by "dynamic this binding"? How can "this" be dynamically bound, yet behave "like an implicit parameter with lexical scope" (as you wrongly claim) at the same time? Is Brendan Eich and everyone else in the JavaScript and TypeScript communities mistaken, and they foolishly added fat arrow functions to JavaScript for no reason, but nobody pointed out that embarrassing mistake until you came along? If you're right, then you're barking up the wrong tree by arguing with me about it, so by all means, get on Twitter and tell Brendan Eich himself, ASAP! Your argument is with him and everyone else, not me. Maybe it's not too late to turn that ship around, but in my opinion it's already sailed. But if you're wrong, then you probably have a lot of bugs to fix in your code, and should stay off Twitter. If you truly believe in your heart of hearts that "this" is lexically scoped, you have definitely proven my and Brendan's point that "this" is a terrible "oft-fired footgun" that causes lots of deep confusion and insidious misunderstanding: just take a step back and look at how sure you are of yourself. Because "this" is certainly more mysterious and dangerous than YOU believe it is.

goto11 7y ago
Regular JavaScript functions work as if there is an implicit "this" parameter (which gets the value from the left-hand side of the call expression rather than the argument list). Fat-arrow function on the other hand does not change "this", which means the "this" binding inside a fat-arrow function is the one from the containing scope. But in both cases the scope of the "this" binding is lexical. Dynamic scope means something different. Dynamic scope means that a variable binding from the call site is visible in a called function and down the call stack. This is not how "this" works. The "this" binding at the call site is never visible inside the called function, unless the called function happen to be nested inside the same lexical scope. "this" is confusing because it gets rebound at every call, even if the function is not called using dot expression. But it is not because of dynamic scoping.