What do you think about a C# 6 like nameof() expression for

guest271314 guest271314 at gmail.com
Sun Jun 16 04:00:24 UTC 2019


```
const x = nameof y
const y = 1;
```

At line 1 adjacent to ```nameof``` how does the user even know that there
is a variable that will be declared named ```y```?

What is the output of ```x``` where there is no variable named ```y```
later declared?

```
const x = nameof y
const z = 1;
```

On Sun, Jun 16, 2019 at 12:03 AM Ron Buckton <Ron.Buckton at microsoft.com>
wrote:

> > What should occur where the code is
>
> It would be "y" in all 3 places.
>
> > ... is a proposal for _more_ than only getting the _name_ of an
> _declared_ and _initialized_ variable?
>
> It is a proposal for getting the name of a _declared_ variable. Whether it
> is _initialized_ does not matter.
>
> > Should a ```RefefenceError``` _not_ be thrown simple because
> ```nameof``` is used?
>
> No, an error is not thrown. ECMAScript is much more nuanced. Block scoped
> variables from 'let' or 'const' exist and can be *referenced* (via closure
> or export, currently) anywhere within the same block scope, even before
> they are initialized. Until they have been *initialized* (the line of code
> contain the declaration has been reached and evaluated), they exist in a
> "Temporal Dead Zone" (TDZ). Attempting to *dereference* them (i.e. access
> or store a value) while in this TDZ is what results in the ReferenceError.
>
> At no point does the `nameof` operator *dereference* the variable, so no
> error need be thrown.
>
> From: guest271314
> Sent: Saturday, June 15, 4:29 PM
> Subject: Re: Re: What do you think about a C# 6 like nameof() expression
> for
> To: Ron Buckton
> Cc: es-discuss at mozilla.org
>
>
>
>
> What should occur where the code is
>
> ```
> const x = nameof y
> await new Promise(resolve => setTimeout(resolve, 100000)); // should x be
> "y" here?
> await new Promise(resolve => setTimeout(resolve, 200000)); // should x be
> "y" here?
> await Promise.all([new Promise(resolve => setTimeout(resolve, 300000)),
> ...doStuff()]); // should x be "y" here?
> const y = 1;
> ```
>
> ?
>
> The immediately invoked arrow function example (where a
> ```RefeferenceError``` is thrown) appears to demonstrate that to output the
> expected result of ```nameof``` within the context of the code example
>
> ```
> const x = nameof y
> const y = 1;
> ```
>
> is a proposal for _more_ than only getting the _name_ of an _declared_ and
> _initialized_ variable?
>
> Should a ```RefefenceError``` _not_ be thrown simple because ```nameof```
> is used?
>
> On Sat, Jun 15, 2019 at 11:16 PM Ron Buckton <Ron.Buckton at microsoft.com>
> wrote:
>
> ```
> const x = nameof y
> const y = 1;
> ```
>
> `x` would have the value “y”. It would not matter if `y` were initialized
> or had yet been reached during execution. It does not deviate from the
> purpose of `let` or `const`, because you are not accessing the *value* of
> the identifier.
>
> Also consider that this is legal ECMAScript in a module:
>
> ```
> export { y }
> const y = 1;
> ```
>
> The binding for `y` exists within the same block scope, it just has not
> yet been initialized. Exporting it via `export { y }`, closing over it via
> `() => y`, or accessing it via `nameof y` would all be the same. In all
> three cases you are accessing the **binding** of `y`, not the **value**
> of `y`. Even in the `() => y` case, you don’t access the **value** of `y`
> until you execute the function.
>
> *From:* guest271314 <guest271314 at gmail.com>
> *Sent:* Saturday, June 15, 2019 3:57 PM
> *To:* Ron Buckton <Ron.Buckton at microsoft.com>
> *Cc:* es-discuss at mozilla.org
> *Subject:* Re: Re: What do you think about a C# 6 like nameof()
> expression for
>
> > Sorry, I meant to say “not entirely correct”.
>
> You have not yet confirmed if in fact the expected output is referencing a
> variable declared using ```const``` on the current line _before_
> initialization _on the next line_.
>
> That example appears to deviate from the purpose and usage of ```const```,
> beyond the scope of ```nameof```, and if were implemented, a
> ```ReferenceError``` should _not_ be thrown when a ```const``` variable
> that has yet to be initialized _on the next line_ is referred to _on the
> current line_?
>
> Aside from that example, the code which essentially already implements
> ```nameof``` should be able to be found in the code which implements
> ```ReferenceError``` relevant to ```const```.
>
> On Sat, Jun 15, 2019 at 10:47 PM Ron Buckton <Ron.Buckton at microsoft.com>
> wrote:
>
> Sorry, I meant to say “not entirely correct”.
>
> *From:* Ron Buckton
> *Sent:* Saturday, June 15, 2019 3:03 PM
> *To:* guest271314 <guest271314 at gmail.com>
> *Cc:* es-discuss at mozilla.org
> *Subject:* RE: Re: What do you think about a C# 6 like nameof()
> expression for
>
> > At that point in the example code the identifer ```y``` does not exist.
>
> That is not entirely incorrect. The identifier `y` exists, but its binding
> has not been initialized, otherwise you couldn’t refer to y in this case:
>
>
>
>
>
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