# Providing property values

There are several supported ways to pass property values for placeholders in [message template](https://vostok.gitbook.io/logging/concepts/syntax/message-templates) when using [logging extensions](https://vostok.gitbook.io/logging/concepts/syntax/logging-extensions).

### 1. Pass property values as optional object arguments:

```csharp
log.Info("Welcome, {User}. You have {UnreadCount} unread messages.", "Jenny", 2);
```

Property names are inferred from placeholders in message template. 

If arguments count exceeds template placeholders count, excess arguments are named with numbers denoting their positions:

```csharp
log.Info("Welcome, {User}.", "Jenny", "foo", "bar");
// produced event properties: {"User": "Jenny", "1": "foo", "2": "bar"}
```

If provided arguments count is not sufficient to account for all template placeholders, the names for existing arguments are still inferred.

{% hint style="info" %}
Strictly speaking, this approach does not support multiple occurrences of the same placeholder name within a message template (last matched argument wins):

```csharp
log.Info("Welcome, {name}. {name}, you have {count} unread messages.", 
    "Jenny", 10);
// The result is: "Welcome, 10. 10, you have  unread messages."
```

Although it's safe to use if all duplicate placeholder occurrences in the template are located far enough not to get matched to any arguments:

```csharp
log.Info("Welcome, {name}. You have {count} unread messages, {name}.",
    "Jenny", 10);
// The result is: Welcome, Jenny. You have 10 unread messages, Jenny.
```

{% endhint %}

###

### 2. Use a single object with named properties:

```csharp
 log.Info("Welcome, {User}. You have {UnreadCount} unread messages.", 
     new {User = "Jenny", UnreadCount = 2});
```

When using this syntax, user is responsible for making sure that object property names match the names of placeholders in message template.

### 3. Use positional placeholders:

```csharp
log.Info("Welcome, {0}. You have {1} unread messages.", "Jenny", 2);
```

Despite being somewhat deprecated nowadays, this syntax enables gradual migration from libraries that do not support structured logging.

It also supports multiple occurrences of the same placeholder within a single template:

```csharp
log.Info("Welcome, {0}. {0}, you have {1} unread messages.", "Jenny", 2);
```

### 4. Use interpolated strings with C# 10:

```csharp
var User = "Jenny";
var UnreadCount = 2;
log.Info($"Welcome, {User}. You have {UnreadCount} unread messages.");
// produced message template: "Welcome, {User}. You have {UnreadCount} unread messages."
// produced event properties: {"User": "Jenny", "UnreadCount": 2}
```

When using this syntax, user is responsible for making sure that new C# 10 features are enabled and Vostok.Logging.Abstractions library targets .NET 6.

It also supports [standard formatters](https://docs.microsoft.com/en-us/dotnet/csharp/language-reference/tokens/interpolated#structure-of-an-interpolated-string):

```
log.Info($"Welcome, {User,10}. You have {UnreadCount:D5} unread messages.");
```

If you want to disable automatic properties extraction from an interpolated string directly cast it to the string:

```
log.Info($"Welcome, {User}. You have {UnreadCount} unread messages.".ToString());
log.Info((string)$"Welcome, {User}. You have {UnreadCount} unread messages.");
```

Or disable it entirely for your application:

```csharp
LogExtensions_Interpolated.Enabled = false;
```

However, in this case, you may have performance issues (due to the internal templates cache) or corrupted messages (due to the rendering stage). See [Message templates](https://vostok.gitbook.io/logging/concepts/syntax/message-templates) documentation for details.

For the same reasons, do not pass properties with invalid names (such as function calls). Instead of:

```csharp
log.Info($"Welcome, {User}. You have {Random.Shared.Next()} unread messages.");
// produced message template: "Welcome, {User}. You have 623653080 unread messages."
// produced event properties: {"User": "Jenny"}
```

you should use:

```csharp
log.Info($"Welcome, {User}. You have {{RandomNumber}} unread messages.", Random.Shared.Next());
// produced message template: "Welcome, {User}. You have {RandomNumber} unread messages."
// produced event properties: {"User": "Jenny", "RandomNumber": 623653080}
```


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