This gist uses a decorator to create a `HashedValue` object from the result of the `$hasherContext->make()` function such that it is possible to determine if a string has been hashed.

hash.php

<?php
// Use a value object to represent Hashed Values (for example passwords)
// this way we can deterine if a string has been hashed before or if it needs hashing

class HashedValue {
    private $hash;

    public function __construct($hash = '')
    {
        $this->hash = $hash;
    }

    public function __toString()
    {
        return $this->hash;
    }
}

trait HashPassword {
    // TODO make it customizable
    // protected $propertiesToHash = ['password'];

    public function setPasswordAttribute($password)
    {
        $this->attributes['password'] = $this->hashedVersionOf($password);
    }

    public function getPasswordAttribute($password)
    {
        return $this->hashedVersionOf($password);
    }

    public function hashedVersionOf($value)
    {
        return ($this->isHashed($value)) ? $value : $this->hash($value);
    }

    public function isHash($value)
    {
        return is_a($value, HashedValue::class);
    }

    public function hash($value)
    {
        return Hash::make($value);
    }
}

use Illuminate\Contracts\Hashing\Hasher;

class HashedValueHasher implements HasherContract {
    private $hasher;

    public function __construct(HasherContract $hasher)
    {
        $this->hasher = $hasher;
    }

    public function make($value, array $options = array())
    {
        $hash = $this->hasher->make($value, $options);

        return new HashedValue($hash);
    }

    public function check($value, $hashedValue, array $options = array())
    {
        return $this->hasher->check($value, $hashedValue, $options);
    }

    public function needsRehash($hashedValue, array $options = array())
    {
        return $this->hasher->needsRehash($hashedValue, $options):
    }
}

use Illuminate\Support\ServiceProvider;
use Illuminate\Hashing\BcryptHasher;

class HashVOServiceProvider extends ServiceProvider {
    protected $defer = true;
    public function register()
    {
        $this->app->singleton('hash', function() {
            $bcryptHasher = new BcryptHasher;;
            return new HashedValueHasher($bcryptHasher);
        });
    }
}