Re: Struct assignment fails, why?

[Brian via Digitalmars-d-learn]

On Wednesday, 16 June 2021 at 20:54:07 UTC, H. S. Teoh wrote:
On Wed, Jun 16, 2021 at 08:44:46PM +, Brian via 
Digitalmars-d-learn wrote: [...]

struct item
{
string name;
int type;
};

[...]

new_item = { "item1", 1 };


The {...} initializer syntax is only available in variable 
declarations, e.g.:


item i = { "item1", 1 };

You cannot use this syntax in assignment statements.

A simple alternative is to use constructor syntax for 
constructing an instance of the struct:


new_item = item("item", 1);


T


Gotcha. Thanks.

~Brian

Re: Struct assignment fails, why?

[H. S. Teoh via Digitalmars-d-learn]

On Wed, Jun 16, 2021 at 08:44:46PM +, Brian via Digitalmars-d-learn wrote:
[...]
> struct item
> {
> string name;
> int type;
> };
[...]
> new_item = { "item1", 1 };

The {...} initializer syntax is only available in variable declarations,
e.g.:

item i = { "item1", 1 };

You cannot use this syntax in assignment statements.

A simple alternative is to use constructor syntax for constructing an
instance of the struct:

new_item = item("item", 1);


T

-- 
Everybody talks about it, but nobody does anything about it!  -- Mark Twain

Struct assignment fails, why?

[Brian via Digitalmars-d-learn]

Hello all --

I have a question about assigning to structs.

I want to be able to create an array of structs that may contain 
different contents depending on user input. I have reduced the 
test case down.


The following fails to compile:

```d
import std.stdio;

struct item
{
string name;
int type;
};

item[] items;

void main(string[] args)
{
item new_item;

for (int i = 0; i < args.length; i++) {
if (args[i] == "item1") {
new_item = { "item1", 1 };
} else if (args[i] == "item2") {
new_item = { "item2", 2 };
} else {
new_item = { "item3", 3 };
}

items ~= new_item;
}

for (int i = 0; i < items.length; i++)
writeln(items[i].name);
}
```

This fails (dmd 2.097) with the following:
```d
struct_bad.d(17): Error: found `}` when expecting `;` following 
statement
struct_bad.d(17): Deprecation: use `{ }` for an empty statement, 
not `;`
struct_bad.d(18): Error: found `else` when expecting `;` 
following statement
struct_bad.d(19): Error: found `}` when expecting `;` following 
statement
struct_bad.d(19): Deprecation: use `{ }` for an empty statement, 
not `;`
struct_bad.d(20): Error: found `else` when expecting `;` 
following statement
struct_bad.d(21): Error: found `}` when expecting `;` following 
statement
struct_bad.d(21): Deprecation: use `{ }` for an empty statement, 
not `;`
struct_bad.d(24): Error: found `items` when expecting `;` 
following statement

struct_bad.d(24): Error: found `~=` instead of statement
struct_bad.d(30): Error: found `End of File` when expecting `}` 
following compound statement
struct_bad.d(30): Error: found `End of File` when expecting `}` 
following compound statement
struct_bad.d(30): Error: found `End of File` when expecting `}` 
following compound statement

```

However, a slight tweak allows the code to compile and work 
correctly.

```d
import std.stdio;

struct item
{
string name;
int type;
};

item[] items;

void main(string[] args)
{
for (int i = 0; i < args.length; i++) {
if (args[i] == "item1") {
item new_item = { "item1", 1 };
items ~= new_item;
} else if (args[i] == "item2") {
item new_item = { "item2", 2 };
items ~= new_item;
} else {
item new_item = { "item3", 3 };
items ~= new_item;
}
}

for (int i = 0; i < items.length; i++)
writeln(items[i].name);
}
```

I guess I am unclear as to why the first fails and the second 
succeeds.


TIA.

~Brian