主文件夹和子文件夹的不同命名空间

Is it possible to do something like:

"psr-4": {
    "App\\": "src/",
    "Tech\\": "src/Tech/"
}

As you see there is App namespace for src folder but in src/Tech/ must be another just Tech namespace. I have tried it but always getting error:

Cannot declare class, because the name is already in use

Yes, it is possible, although I don't know any good reason to do such thing - it just makes harder to understand namespaces structure.

The error Cannot declare class, because the name is already in use is probably caused by FQN ambiguity, for example if you have file:

<?php

namespace App;

use Tech\MyClass; 

$myClass =  new MyClass();

And you have App\MyClass then import for MyClass is ambiguous - new MyClass() could either mean new \App\MyClass() or new \Tech\MyClass(). You need to use aliases in this case:

<?php

namespace App;

use Tech\MyClass as TechMyClass; 

$myClass =  new MyClass();
$myTechClass =  new TechMyClass();